AITA for buying my son a halloween costume?

I(34F) and my husband(35M) have a 5 year old son together. My husband was raised in a family where boys play with cars and girls with dolls. Son has a huge obsession with unicorns and asked if he could go as a unicorn for Halloween. My husband told him no and he would take him shopping for a boy costume.

I found one in his size and wrapped the costume up to surprise him. I gave it to him after school and he immediately went to put it on. My husband looks at me and tells me that I am trying to change our son to be girly and should have bought him a spiderman or superman costume. This incident happened over the weekend and husband is still fuming over it.

AITA for buying my son a halloween costume?