Alleging a violation after he asked for an API key, rather than simply turning him down or saying that he could experiment but that he would need to get agreement before deploying, seems like defamation to me.
True, but accusing him of a violation privately, to him, is not defamation. Accusing him publicly is still probably not defamation. Whether he violated certain terms of service is something that would ultimately need to be decided by a court, so them believing he did so isn't defamation even if they're wrong.
