Have you contacted PlusBus to tell them that their website is wrong, or just going to keep blaming the bus company?
The bus company haven't "made up" an exclusion. It's not fictional. It's an actual restriction, clearly advertised on the relevant page of the bus operators website -
https://www.firstbus.co.uk/york/plan-journey/live-local-spend-local-travel-local/york-city-fc - that only the specifically listed tickets are valid on Y22.
The bus driver certainly hasn't done anything wrong.
I could sell you a ticket and tell you that it's valid on the TrentBarton "Red Arrow" service. But it wouldn't be, and the driver would rightly reject the ticket, and the company would back up the driver if you complained to them.
In this case, I'm afraid, your issue is with the promoter, not the bus company.
That's not to say that there aren't other issues with PlusBus acceptance in general - there clearly are - but in this instance it's the PlusBus website that's wrong, not the bus company or bus driver.