That is way too hostile for a first contact. It would be much better, at first, to politely ask them to comply with the license. If they ignore you, or refuse, then think about escalating.
Maybe. If it's just removal of the other info, then perhaps. If it's removal AND implying it's theirs? No, not too hostile at all, in that case.
Based on the commits, PRs, and issue history, they were all previous issues that exists in OasysDB. They changed the name of the contributors to their own.