but we can't really call that speculation because speculation is supposed to be based on facts not based on guesses. speculation itself can be a guess but the basis must be facts. in this case when you see coins move you would be making 2 guesses and them making a conclusion. the first guess that nobody mentioned is that you are guessing it moved to "an exchange". the fact is you don't know where they moved. it may just be to another wallet, or it may even be sold off the market not on exchanges. and the second guess that others also said is that you are guessing they were "sold"! for example when someone moves coins to an exchange it may be to put up a fake sell wall preventing the rise so that they can BUY more.
I'd say it still fits the definition:
the activity of guessing possible answers to a question without having enough information to be certain
You know the coins moved somewhere (and there are tools that may tell you where), so in the end you're speculating on a possible outcome of an action. I don't think the semantics matter either way though lol. People won't stop doing this for as long as whales maintain their reputation, which they may not deserve to the same extent anymore given the size of the market.