That's true, but it doesn't change your parent's point - this cannot be called "open source" at all.

That will be helpful with my open source projects. Thanks.

In a general sense, yes. However, I really don’t see how this would fall into that category. It looks like someone has a copy illegitimately and is trying to reimplement it.

Yes. AIUI, it's the illegitimate copy that's the problem, not so much the decompilation approach.

Wait, there are EU regulations on this topic? I understood there wasn’t a common framework, and instead each countries in the EU have their own approach.

Edit: I was wrong, I found the following: https://en.wikipedia.org/wiki/Computer_Programs_Directive

> (Art. 5). The legal owner of a program is assumed to have a licence to create any copies necessary to use the program and to alter the program within its intended purpose (e.g. for error correction). The legal owner may also make a back-up copy for his or her personal use. The program may also be decompiled if this is necessary to ensure it operates with another program or device (Art. 6), but the results of the decompilation may not be used for any other purpose without infringing the copyright in the program.

It's actually really old, in that this bit goes back to the 1991 Directive, not just the replacement 2009 Directive.