Why not believe it, though?
It is pretty obvious that within the world of gambling and cryptocurrency there are people who have enough money to gamble such big figures in a single session. I am not saying OP actually did so, but the possibility of what he says is not out of the boundaries of one can see people doing if they are rich.
All of us have read stories about starts and billionaires flushing down the toilet millions in a casino and we all believe it, since there are well known personalities. Op could easily be a Bitcoin early investor who felt like venting (or bragging, depending on your point of view) about his deep pockets.
Though, I agree with your advice, whether he is rich or not, anyone losing that amount to a casino should reconsider their habits, otherwise, there future will get dark before they even realize it.