This is a hard fast rule. No exceptions.
If a guy calls himself "Alpha", he is a beta.
It takes a fair amount of false bravado for a guy to insist he is an Alpha. A true Alpha never needs to insist he is an Alpha and sees the pointlessness of trying to actually insist they are Alpha (actions speak louder than words, and in some cases, counteract them.)
So, simply, if a guy insists he's an Alpha, he's not. End of story.