I remember several projects that are listed on the exchange before being distributed to bounty hunters. The price in this case also fell immediately after the listing.
I do not even know where the whole idea of the bounty participants being the ones dumping on the market started from. Probably some big investors trying to use that as a tactics to remove the eye of the community from them. Whales are always responsible and it is not like the whole bounty participants amount put together will really make much impact anyway since some give as low as 1% of total contributed during ICO and 1% is nothing as far as I am concerned.
Most of the good projects already implement a kind of lock in period where they distribute the bounty and airdrop tokens after they are already doing to the investors.So it's nothing new
Devs already know gradually the bounty participants were never the fault since so far, some participants never get to receive their token until it has been listed for a long time and still, the price of the token gets to drop. Those who dump on the market are the ones holding the larger share of the market, and since they were fortunate to get a whole lot during the bonus period and pre phase, they had a lot on them to dump at once.