I think that bet was just to attract other bettors to follow him and I'm sure a lot of them did just like that as sheep effect can be huge sometimes , especially if a superstar promotes it. Personally, I will never follow someone known regarding bets because they can afford to lose and also they're doing for entertaining and maybe for the bookies but wagering with BTC in that amount it's just wow and I'm sure he has a lot of cryptocurrencies if he made that bet.
Overall , it was a great promo for both BTC , Super Bowl and even bookies as well and a bad one of gamblers haha.
Without a doubt this was done in order to promote himself, but that is not bad on itself, after all famous people live out of their image so if he wants to project the image of a big gambler with cryptocurrencies then that plays in our favor, after all despite the popularity of bitcoin many still think of it as nothing more but an investment, if they can see they can do a lot of stuff with it then they will begin to think out of it as a currency, and that is a good thing as that is exactly what bitcoin is.