It still uses trademarks from ACF, those are obviously not "open source", which also has been Matt's & wordpress.org's stance since forever: the _code_ is GPL, but the assets are not.

If you "fork" the assets, you're not covered by GPL.

Obviously it's nonsense to discriminate between the free version of a freemium plugin and a commercial plugin and this is simply a stupid way to lash out.

Because WordPress is licensed under the GPL, all plugins must be licensed under GPL-compatible licenses. This applies to ACF Pro as well.