AA is a game that is a normal full sized game, but was made on a budget that limited scope. Good examples are the Metro series or Balatro. AAA is your normal games with big budgets. AAAA is a special title for Skull and Bones, it means you spend a gigantic amount of money and make sure the whole thing sucks.
Balatro has a publisher, Playstack. While they put very little money into traditional advertising, Playstack absolutely had a calculated marketing campaign that nailed success by getting specific streamers on board.
This technically makes it not 'indie' as they have a publisher but the indie/AA/AAA labels are kind of ridiculous.
I believe the AAA term actually originates from investing. In investing, a "AAA" investment is one where everyone is pretty confident that it'll be a positive return. It got a bit of use in the games industry to mean games that were expected to sell well no matter the what. It eventually got warped into just meaning big games with big budgets, and people started using the "AA" term to mean "like AAA but not as much"
I'd bet on JRPG rank rules; D, C, B, A, A+, A++, S, S+ and as many S' they bloody want in order to make S tier worthless. Instead of doing the sane thing and adjusting the criteria for a rank.
But in this case there is no Ds Cs or Bs, only As.