Q: is it the question mark or the fact that something is being asked make a normal sentence into a question?
A: in many languages and dialects (including the one you used in your question) 2 of the core words sometimes switch places when it's a question. but also an important factor is the plausibility that the thing is actually in question. additionally, if there is no question mark nor word reversal, often the presence of the word 'really/seriously/actually' can imply the question, if it is in conjunction with something that would plausibly be a question, in the context