The Adweek source linked goes into a little more about it, but not much. Specifically mentioning a model was used for lyrics first, then the AI created a melodic and percussive arrangement. It doesn't say much more about how it was done.

I found another article that states they had a real human voice sing the lyrics (then auto-tuned it to Scott's style), but there's no actual sources here, or on any other articles I can find.

https://musebycl.io/digital-data/agency-used-ai-make-travis-...

I did follow through to Adweek, but given that it is Adweek and not NME, I wasn’t sure how literally to take the word “arrangement” there :-) Thanks!

See the adweek article that was linked in OP's article, it has more details. The AI part was only lyrics, melodies, and percussion arrangements; not actually the production itself.