My dad just had a heart artery stent operation and is drinking

I know this isnt the right reddit for this, i just didnt know if anyone had personal experience. My dad just had a heart artery stent operation, and before we put him in the car the nurse stated after he asked, to not drink for the next 24 hours. Despite this, right when we got home, despite me asking multiple times not to, he just started drinking a beer saying it wont make a difference. Will it? I find it frustrating how he wont even try to follow basic instructions given, how bad is it? He is drinking corona light beer. 473ml, only a single can but it still worries me.