Yes, it is called a license violation, and with things like Github these days, you might not just want to run
sed through someone else’s source code and replace strings! See the github issue, and the commit fix.
Irrespective of other accusations of plagiarism, if people are thinking about open sourcing their code, they need to abide by open source rules. Some of this is legal (like this case), some of it is governance related, and some of this is community related.
As always, for consulting about open source, don’t hesitate to drop me a line.