It seems more like:

1. Delve Labs has commercial scanners which bundle but do not link with WPScan.

2. WPScan, previously licensed under the GPL, introduce a commercialization clause in addition to the GPL.

Side Note. WPScan may not have the right to do this because they do not use copyright attribution. Without this they need permission from everyone who has ever contributed code to their project.

3. WPScan demand money from Delve Labs.

4. Delve Labs make a fork from a point before WPScan introduced the commercialization clause. They keep this version licensed under the GPL.