Nope.
The “maverick” brand was affixed to him during his 2000 primary run for the presidency by the DNCMedia—where they were trying to get George W. Bush defeated.
Palin simply called him that after it was a well worn nickname.
Well, perhaps even earlier than that:
https://ktar.com/story/1743462/why-was-sen-john-mccain-known-as-a-maverick/