"CATO" is an acronym because people are using it that way. It doesn't matter if it was originally an abreviation. Language, especially informal language, isn't written in stone. It changes over time.

"CATO" is an acronym and "cato" is an abbreviation. Both are used interchangeably and each is as correct as the other.

Fred can write "cato" as an abbreviation and I won't correct him because that's okay. But, he insists on jumping on everyone who decides to write it as "CATO." And that's not okay.

-- Roger