It's fairly simple as far as I can see. McGregor had a contract with the old company, not with the new one. While he could have chosen to move his contract to the new company, he could not be forced to do so (due to it being a new company).
According to LNS "This is not to say that a Club has legal personality, separate from and additional to the legal personality of its owner and operator. We are satisfied that it does not, and Mr McKenzie (the SPL’s lawyer) did not seek to argue otherwise."
If the club has no separate legal personality then player contracts must be held by the company. So all in all just some simple employment law. Unless I'm missing something I cannot see how this shows one way or the other that Sevco are a new club (they are though, Rangers -a current at the time SPL member club- voted yes to Sevco -not an SPL member club- getting SPL entry - only clubs have votes so they must be two separate clubs).