I'm not offended by your comment. For one, it's not even talking about me or any work that is closely related to mine. I'm just pointing out that someone who was in that situation may perceive the comment negatively, and explain why that might be the case.

It is (genuinely!) good that you did not intend malice with your post. And being aware of sexism, or any other kind of stereotyping/discrimination, is definitely a good start. That said, just because you did not mean to be insulting does not automatically preclude you from coming across that way. While we all make mistakes, and I assume from your comment that you wish to avoid them yourself, I think what your reply here really shows that you did a poor job at expressing what you really wanted to say. This is unfortunate, because it's actually pretty easy to rephrase it to not come across poorly.

You–and this is a fact–noted that the video does not have much technical content. It's kind of a marketing piece, really. A lot of people here (myself included!) would have probably wanted a deeper dive into the technologies involved. Here are some examples of how you might rephrase to convey that:

"It's interesting to see that they got this working, but I have to admit I'm kind of disappointed by the video. There's not a lot of detail as to how this works. I was hoping they would explain the Thunderbolt adapter, at least." (It's rarely a bad idea to be courteous and polite, especially when you start a comment. This conveys your feelings and where you feel the video falls short. The work itself, rather than any people involved, are brought up.)

"What's with the big Thunderbolt network controller? Anyone know what's up with that?" (Invites others to respond if they know the answer. Perhaps even the author or someone closely related! They often browse the internet just like you.)

"This is really just a marketing video :/ It's kind of stupid that they don't actually explain anything that's going on. I hate companies that keep their cards close to their chest." (This has a much stronger opinion in it, and your idea of what they should do to fix it, but it directs it at GitHub, not the people in the video. GitHub is a lot of people but not one person. It's hard to offend a company.)

"Why did GitHub make this video? It has no technical content and makes it seem like these women are not involved in the engineering process. Why bring out the director of this team if you won't even let her say anything about the actual work she did?" (This is a very strong opinion. If you're careful you might be able to play it, but do note that the women in the video may not appreciate you speaking for them about how the video portrays them.)

On the other hand, you said, and I quote, "I got the impression that the guide didn't know anything about what they were talking about w.r.t internals or how it's used". Do you see how this directs your criticism at the people in the video? There are plenty of reasons why they might not go into detail, many of which are out of their control or not relevant. You might have the "impression" that the guide doesn't know what she's talking about as opposed to, say, actually not knowing what she's talking about, but if you go up to someone and say "I get the impression you're stupid" that's basically saying "I think you're stupid" or "you did something stupid". That's not nice, regardless of how you feel about it. From your second comment, your annoyance has nothing to with the people, so why bring them up? Direct your criticism at the thing you care about.

I think a big problem is that people often realize that what they're about to say is difficult to express and can be a sensitive topic (women in tech, here). Unfortunately, saying it anyways and then ducking under "this is hard to describe! I am not being discriminatory! I would say it to white cishet men too!" doesn't actually really help. First off, why would you say it to a white cishet man? Your comment, in a vacuum, doesn't have any sexism in it. It just sucks in general. You probably shouldn't be going around telling men that they give you the impression of not knowing what they're talking about, either! But when you do bring into the picture that women are the target of these comments more often than not, I think you should demonstrate a little more tact. Read it a bit more closely to see who the criticism might be aimed at, and soften or clarify as appropriate. Or ask someone else you trust to help you out!