No proof. Not even provable to anyone here. Just logic. It’s a suspicious low trade, lower than anyone would normally do.... especially on a slow day where it’s not a partial fill.
Just like when you see a series if 10,000 sells over and over, back to back, or the opposite 10,000 buys back to back. Who does that?
You have been trading enough to see when the MM want a stock to go up, you can place an order to buy at the ask, they give you a small partial fill, raise the ask, and as soon as you make the change to the new ask, they do the same thing walking it up.
And again, the opposite is the same. One little sell at the bid, lowers the bid and ask over and over and down she goes.