It sounds like you’re right. I found this article from 2017 about it: https://turnto10.com/news/local/garage-c-at-tf-green-offering-parking-for-peanuts.

TLDR: the RI Airport Corporation leased Garage C from New England Parking until the end of November 2017, when they leased it to Pro Park America, who rolled back the prices.

I love garage c - it’s a good price, a short walk to the terminal, and you get 1 free day of parking for every 7 paid days of parking.