No, that is merely what the US government alleged. There's an allegation from a suspended cop that he is a gang member because he wore a Chicago Bulls hat, and that's all ICE is basing itself on to call him a gang member.

The court said not to send him back to El Salvador because he applied for asylum, and was granted asylum because he faced dangers in El Salvador. Not because he's a gang member, which are allegations that have never been proven.