My 20 yr old bf had a beer and my parents got mad

So my bf was invited to my grandpas party, and there was tons of alcohol around and naturally he just grabbed a beer. I got home and my parents are like did you know your bf had a beer and he’s not even 21! He’s not supposed to do that. I’m like wtf is wrong with you all..... hella strict for no reason. It’s not even like he drove.