Apparently this is not about software licensing so much as about the services Rebble provides:

Core would spearhead the development of brand new watches, and we’d be there to provide our Rebble Web Services to go with them.

It now seems Core wants to just keep on using these services as their own. I read a few paragraphs but I gave up when they go back 9 years to explain it all.

But this isn’t the first time a company tries to steal what isn’t theirs, under the auspices of FOSS, and my benefit of the doubt definitely stands with Rebble here.