yeah, it could be that he just loves to bet for his favorite team. but seeing how high rollers gamble on gambling sites, I don't think him betting that much money equals being "too confident on who is going to win", for all we know that is how he normally bet on sports betting.
Drake has a history of betting huge amounts of money and he is also losing a lot of bets in the past, it's pretty normal for him, we all know that excessive gambling can become a downfall of these celebrities who are very much into gambling, the income can stop but their addiction to betting will not, he can still sustain it because he can still make a lot of money but if he is not a celebrity crowd drawer no more he'll regret all the money he loses from gambling.
I also believe that he may have won that amount, but of course, he will not post his losses.
I don't think stake has something to do with his post, if he is a regular player on the site, sometimes it is just normal for them to post something like that.
But if stake knows about Drake being their regular patron, they may reach him for potential collaboration. Who knows?
Other celebrities who are into gambling may follow where he is betting, as they are now confident that stake can handle such amount.