He has WAGERED half a million dollars, doesn't mean he owns it. Even if you owned 138 BTC you can't manipulate anything, not even on 1 exchange much less global BTC price!
Judging from my own very small balance and wagering, I generally manage to wager around 30x my deposit minimum before busting, and that's without a conservative strategy. Conservative should be close to 90x so maybe he has 50k worth of BTC. Anyway, if the guy is smart, he is wagering conservatively and taking advantage of RP bonus plus Wager bonus to reduce his 5% house edge to about 4%. I suppose he will maximize his free rolls too, so maybe that even goes to 3.5% With the prize of 10k, that's 1.5% house edge. With lotteries, that's back to 1%, maybe even lower and close to 0.
30x sounds about right for stratetgyless gambling.
He could even be in profit from his rolls or maybe did a strategy of just gambling with the profits and took out the rest.
It'd tske about 50
BTC to get the coinbase pro price up by about a dollar. And there there'll be a load ofblimit orders higher up so I'd say a few thousand Bitcoin would be needed to push the price up by a hundred dollars or so.