im not an lawyer, but his rights were definitly violated. If you create something, then under German law there is the so Called "Urheber" who cannot give up rights. So copyleft licenses need to be rewritten to accomodate this.
Additionally they cut out the text of the license, without an reference wat the license means. I don't think that is completly OK. Most write an link to an source url if they don't want to enter a full license text.
It’s more about that he thinks he will get the money for the lawyer back but that’s not the case if you just go for a „Abmahnung“ without further proceedings.
If an lawyer in germany does or propose something he is in trouble. An license is not cheap and hard to aquire plus reputation is money and an laywer loses both if he acts or proposes things that harm the client.
Additionally they cut out the text of the license, without an reference wat the license means. I don't think that is completly OK. Most write an link to an source url if they don't want to enter a full license text.