I think the betting bump is from horse racing's "big fight" effect. The Derby is now a trendy thing to do.
The NBC coverage leaned as far away from handicapping...and toward celebrity watching and lifestyles of the rich and famous...as I've ever seen. After the race, when the talking heads came back from a 10-minute commercial break, the stands behind them were empty even though there were two more races on the card. "Show over. See you next year."
The double-header with the fight probably helped, but either way the boost is likely a one-day phenomenon.