They can because that statement isn't binding and it's very interpretable.
> Adobe does NOT train any GenAI models on customer’s content
Today? Right as the tweet was being posted? That he knows of? They train non-GenAI models? Opinions are his own? He's not an authoritative source? It's not "customer content" if you gave them full rights on it?
We have evidence of tweets not counting much in a court, particularly if there are deep pockets behind them. So no, unless it's a legally binding document (and even then I have my doubts, deep pockets run deep) it's literally just words.