It happens though in real life. Stan Musial hit 5 HRs by himself in a game. The Blue Jays and Orioles combined for 10 HRs in a game in 1987. Wade Boggs hit 24 HRs in 1987.
I wouldn't make any big decisions on sliders or saying "something is broken" based off of a small sample size of games, especially one game where you tee'd off on a guy.
Go 20-25 games, then if you think HRs are happening too often adjust the power slider down a notch or two.