Has anyone seen this before??

I was playing on 2fort messing around with scout, I saw a red pyro coming out of blue spawn with other players and thought it was a spy, so I engaged, after hitting the “spy” with mad milk he turns into a soldier and kills me. I’ve never seen anything like this before in my playtime and I asked my friend with 2K hours if he’d seen it and he said no. Does anyone have any idea what this is?