I think we can assume that this ITT has been issued because Scotrail have been told that the 22x fleet will be available then and have been offered them. They're simply following due process.
I'd imagine that this is indeed the case. I did say in another of the ScotRail HSTs threads in September that any tender issued would worded in such a way that only the 222s would meet the requirements. There is no other intercity diesel fleet that would be available within the specified timescales of the tender.