are they like wifi headphones or...?

Yeah with older technology that happened often but today's stuff doesn't typically do that.

I remember when cordless phones first got big, it was pretty normal that you could hear other peoples' conversations, either just a light static or sometimes very clearly. BUT they could not usually hear you.

When metal teeth fillings for cavities were normal, many people claimed they could hear local stations as well, the classic actress, Lucille Ball, even helped bust a nazi cell near Los Angeles when her fillings picked up radio transmissions during WW II.