I notice my mind tends to think this way as well. Thinking about why I will think that usually yields recollections of people making "innocent" observations while they clearly had ulterior motives; such memories are in-person events, not this sort of interaction online. That said, it's easy to (read: difficult not to) apply similar heuristics to online interactions.

Not to excuse it; I agree with your conclusion. Hopefully such an understanding can help people to be patient with the behavior despite the annoyance.