If you teach someone about music theory by listening to Stairway to Heaven, and then they write their own song that starts with an A minor chord... are they violating copyright of Stairway to Heaven?

Copilot isn't sampling. Sampling is literally copying snippets of someone else's music and putting it into your music. Copilot doesn't do that. There's no giant database of text that it just slurps suggestions out of.