Earlier quoted context omitted.
ACF isn’t a premium plugin (linked post only concerns those). The linked post also might not reflect the current policies. This update was a security update and was done due to the unique circumstances around the original publisher.
Exactly. ACF is free and open source. ACF Pro is not. Secure Custom Fields is based on the free version (ACF, without "Pro").
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.