I was wondering if the patterns are also under the gnu license since
it's not source code?
Yes, the patterns are under GPL. The GPL license for the patterns
appears in the files themselves, see any file in the patterns/
directory.
And yes, they are source code. The patterns are fed to a compiler
to produce C code.
From mkpat.c:
/* Compile one of the pattern databases. This takes a database file,
* e.g. patterns.db, and produces a C code file, in this case
* patterns.c.
*/
So the patterns themselves are a sort of language.
The files that are not under GNU license are gtp.c and gtp.h.
Everything else is GPL 3.
Dan