I think it’s more of the old Bitcoin investors back from 2010 that now own $100M or more in Bitcoin,than new institutional investors for the following reasons;

1. Old Bitcoin investors have done this 20times in the last 8years,so they will surely do this again.
Institutional investors have done this before.Although,they have probably done this with stocks a few time before now,however it is very illegal with stock,so doing that is not something many people would do.

2. Old Bitcoin investors don’t care. No one knows who they are and it’s very unlikely for them to get caught.Also,it’s not really illegal to manipulate Bitcoin prices because its legislation is still unclear and a grey area.
Institutional investors have to play by the book,they have company guidelines,CEOs and board members,rather unlikely that rogue employee dumps all these Bitcoins without anyone knowing.If this were really an institutional investor,the whole board,CEO,employees would need to be complicit,which will just  doesn’t make sense.
Sure,it’s not illegal per say but institutional investors have more to lose here than to gain.For them,crypto is still a testing ground and they don’t have too much money in it.

3. Institutional investors would need to own Bitcoin in the first place before they could dump them.
Over the last 6months Bitcoin has been very stable and there was too much of an opportunity to buy large amounts.
Sure,there were a lots of OTC purchases,but they also affect the market,Old Bitcoin investors already own the Bitcoins and they can sell them at will.
Furthermore,i don’t think it is institutional investors but rather old Bitcoin whales getting back into the Bitcoin manipulation game.

However,i think that the Bitcoin whales have told institutional investors what they are up to,they have likely told them through the grapevine that they will dump the price to $4,xxx,so that they have institutional investors with them in order to have a stronger pump.
In all,i believe this doesn’t incriminate institutional investors at all because they know what’s going on in the market.