An unsatisfying answer since Thunderbird wasn't around long enough to demonstrate how in sync with the land he was, but I think this is really the only possibility

Edit: I just realized he must be thinking of Garok the petrified man (the person that ended up being the catalyst in the issue) and not some other candidate. I don't think he's a mutant and idk how Havok knows about him, but he does have a connection with the land and he was thought dead