Sorry to spoil your conspiracy theory, but he was in line for one anyway (in the recent Scotland 'Future' squad).
There was plenty of other players in the future squad who will not be getting a call-up . It's not just when a player moves to the OF, Peter Canero went to leicester, stopped getting a game and then got a call-up. I actually don't think it's overdue, he has alot of improving and, shall we say, 'growing up' to do before he'll be international class.
When a player move to a bigger club the international manager sits up and takes notice and gives them a call-up. It's not as if the player has become magically better over night, it's just the player has a bigger profile. It's no conspiracy, it's just what happens.
Plus, if it's an Old Firm player, their profile is higher than ever. Also, because the national team's management hero-worships everyone who's even been at Ibrox and Parkhead, this works both ways; players who are well past their use-by date, such as Neil McCann, are rewarded with undue call-ups.