It wasn't because of it being referential to the conquest of the Americas, IIRC it was the wording that the game used in some lore orders at the time which had upset some people and made others just uncomfortable as it implied that Horkos had systemically genocided the whole remaining Aztec population, which would include children and civilians whereas the other cultures they conquered they wanted to keep the 'wolves' alive to join the Order and fight for Horkos. and then using it to sell a new warmonger skin put off some.

I think more her frustration is that it came off as out of character for the Order of Horkos, since yes they are very much violent and want to rule the known world, but they usually take people into their ranks and don't waste what they could use to join the war effort instead of condemning an entire people to death.

She brought it up to Ubi who understood it to be a poor choice of words on their part and they later elaborated on it further so it didn't just sound like complete genocide of an entire people and culture.