The “No true Scotsman” fallacy is when you introduce unrelated criteria to disqualify something that would ordinarily be a member of a group. It’s perfectly reasonable to point out that somebody who was not born in Scotland, does not have Scottish family, does not hold any kind of British citizenship, and has never even set foot in Scotland is not, in fact, a Scotsman. That’s not a fallacy.
A sprint is a discrete period of time in which discrete software development tasks happen. A “rolling sprint” is conceptually void. You can’t have a discrete period of time that lasts indefinitely any more than you can have dehydrated water. The “rolling” part and the “sprint” part are mutually exclusive.
I’m not even saying that they weren’t “doing real Agile” – I’m pointing out that what is being described has literally no meaning at all. You can’t be good or bad at it because it’s a meaningless term.