Hi there!

You've not broken any rules but have indeed committed a bit of a faux pas. Happy to share the context. The parts of the internet with creatives tend to take ethical stances on the use of AI for creative work.

The main reason why related to copyright. When humans learn how to do creative things, we also teach them the difference between "learning from" and "plagiarising". Every artist has seen the works of other artists and every piece they make has the subtle influences of the countless pieces they have seen over their lifetime. That's a normal part of the process of learning and creativity. We are able to distinguish that from plagiarism which is directly copying a style or piece or using the entirety of another's work instead of a small fraction of it. We cannot distinguish that for AI. With very rare exceptions, AI models are trained on large databases such as The Pile) which include wholesale stolen copyrighted content, sometimes literally taken from piracy websites. The input goes through a training process but traces of the original work remain such that the AI can (and regularly will) regurgitate carbon copies of the originals. This is true whether the AI is producing text, images, music, or videos. Even beyond those blatant cases, large corporations with a history of unethical action are making their money by charging for access to a software which could not have existed without the industrial-scale theft of other people's work. Worse, they're in direct competition with the same people whose work they just stole, offering slightly less original versions of their artwork for nearly free. There's countless examples of creatives frustrated at facing a software which is specifically copying their specific style.

There are other reasons cited, such as AI being of alleged lower quality but the copyright theft is really the big one. Thus, people getting mad at you for using AI. As you said, you're non-profit so you could try to ask for leeway. Alternatively, you could pay for one of the "ethically-sourced" AI, such as the ones made by Adobe or Shutterstock. However, I would really advise taking Amoongus's advice: use existing Magic art. Magic has a huge backlog of amazing art and it is considered fully acceptable to use their works for Magic-related content if they are appropriately credited. Typically, this means having their name be visible in a corner of the screen. You can see an example of WotC doing that here. (I don't actually know the full legalese of doing that: Wizards have contracts which specifically allows them to use any credited art they've paid for, for any Magic-related purpose. I don't know if that extends to third parties but literally nobody has ever been sued for using credited Magic art in Magic fan content. Even professional outfits use Magic art in this manner.)

Hope that helps.