I think both of them, the thing is if a project is listed on exchange and it exceed the ico price that's when the investors start dumping theirs and it results to the worst of the dump because they have enough to dump, and if it is the other way around that's when you find the bounty hunters doing their thing as far it pays for their efforts.
Especially for the early investors just like those have participated in the pre-sale that acquired a huge bonus and then they cna dump it even the price of coin or token was getting the ico price.
That should be considered as the first party which started to dump their money.