Why does all boys call my brother gay?..

So I'm 13f and my brother is 12 and recently he's been telling me over and over that 5 boys called him gay and some boy at the park (I had to slap and tell off) called him ''bitch-like''. My brother is 5'6 and very gentle and shy and soft spoken but he has lots of female only crushes. But anyway why does everyone call him that?