Depends on the intention I guess. They might have been genuinely worried that the token was going to crash and also didn't trust the counterparty to be able to pay for it. In this case it would have been a genuinely legitimate transaction.
But if dumping the whole stock was done with the intention, even partial, to crash the price, then it seems to me that it would be manipulation. Of course crypto is unregulated, so it wouldn't be illegal.
