I agree with the previous comment, he's 22 years old and if he's still living with his parents - not necessarily something to be ashamed of these days - the parents more likely than not have guidelines for him to follow, as it is their home their rules after all
Burping can happen accidentally, and sex happens by choice. Burping and sex have absolutely nothing in common, so I don't know how you could compare them.
Since you're going to read my post selectively and only choose what you want to hear you shall never know.
I had already said I know it can happen accidentally, and no one said to never burp. However in some cases you CAN hold it in! (Imagine that) and excuse yourself to the next room.
In my house my mom and I have burping contests, I understand it being rude in front of guests or in a restaurant but in your own home, it shouldn't be a big deal.. In my opinion x)