I think something is off with the number or he was placing bets for others.
Generally you have to win at a 55-60% clip to break even/win a little money in sports gambling because of the juice.
So, in order to have bet $45K he either would have needed to lose $45Kish or have won about $25K to have kept betting during the time period. Those are still really large amounts for one student, especially considering his background
Start with $100. Many apps give you free bets for signing up as well but we'll ignore that.
Bet $100, win $100 balance $200
Bet $100, lose balance $100
Bet $100, win...
and so on and so forth. Again, you don't need to have risked lots of money to get an amount that high but you would have to be good enough to have at least broke even. Not all bets have negative vigs, in fact unless you're always betting favorites or spreads, you'll have some bets that will give over 100% returns.