I think his claim is that this particular event should not be called "anthropogenic", in the same way that we can't say that the 2003 European heat wave or Hurricane Katrina or the 2015 snow hell winter (in fact, global warming produces more intense snowstorms) that Boston had are anthropogenic, because the effects of AGW are diffuse, and because erratic and bad weather are not at all new (they'll just become more common with AGW).

Hot weather in Seattle is rare but not that rare. In 2009, we had a beautiful summer in New York (the hottest it got was 93 °F / 34 °C, and most days were around 82 °F / 28 °C) while Seattle shot up to a DC-esque 105 °F (41 °C), setting an all-time record. And for reasons that I don't entirely understand (but are probably related to El Nino) we tend to get a mild summer in the Northeast/Midwest when the Pacific Northwest gets heat, and vice versa (the "vice versa" being the usual pattern). Right now, the Pacific Northwest is baking while it's absolutely beautiful (perhaps a bit cloudy, but I'll never complain about 50s °F in July) in Chicago. Hot weather in Seattle is rare but it isn't a new phenomenon.

Anthropogenic global warming is (almost certainly) real and it's extremely dangerous. The OP is just trying to warn us away from attributing specific climactic events to it. This leads to the "global warming can't be real because it's cold in Buffalo" line of reasoning. Weather has always been erratic, and in a globally connected world, there's always been one kind of hell weather happening somewhere and it's dangerous to try to look for a pattern in it.

Personally, I think it's time to escalate the terminology to climate risk. "Climate change" sounds too mild and climates have been changing forever; the difference is that they're now happening at a level that represents a genuine existential risk, because every time that they've changed this fast for a prolonged period of time, it's triggered an extinction event.

The problem is that most people can't evaluate the risks. Take heat. Most people think that a 10 °F (6 °C) rise in summer temperatures wouldn't kill them. That means that the hottest day in a typical New York summer would be 110 °F (43° C) instead of 100 °F (38 °C). That sounds extremely unpleasant but not fatal, because 110 °F in the desert is no big deal. What few are aware of is that it's not the air temperature ("dry bulb") but the wet-bulb temperature that represents lethality, with 30 °C being acutely dangerous and 35 °C being fatal (the hottest days in the hottest deserts, even with dry-bulb temperatures in the 50s, typically have wet-bulb temperatures in the unpleasant but bearable 20s). One possible risk of global warming is that it'll allow heat/humidity combinations that don't even exist right now (except, on the worst days, in the Persian Gulf). Here's a terrifying link on the matter: http://web.science.unsw.edu.au/~stevensherwood/wetbulb.html . Granted, it puts the numbers at hell settings (12 °C rise) but it still shows us what's possible. This model shows the entire Eastern half of the United States (even stereotypically "cold" places like Bangor, Maine and Milwaukee) becoming uninhabitable, along with almost all of Mexico and four-fifths of South America. Northern Africa, India, the Arabian peninsula, Southeast Asia, Spain and France also become uninhabitable, not to mention the entire Australian continent aside from a southern fringe (which will still be hotter than any place today). Unfortunately, the wet-bulb threat isn't something that most people understand, because when you say "wet bulb temperature of 35 °C (or 95 °F)" most people hear the "35 °C", which doesn't sound that terrifying because, as a dry bulb temperature, that's fairly mild.