OK. Thank you

"Massive" means big. When talking about a friend though, people don't usually talk about their size. They talk about how good a friend they are. So massive here probably means "really good" friend. Having said that, it is an unusual word to use to describe a friend, so it may be meant ironically or at least not very seriously. And since the speaker is pointing out an error, it is probably the speaker's way of trying to be nice while telling someone they are wrong. I hope that helps.