If I'm visualizing this correctly, there was no foul. (A diagram would be very helpful.)

The defined term "fetching" does not apply at a leeward mark.

WP is not required to go "low and slow" - if they continued on port, they would be contrained (since they are the windward give way boat) to sail to the mark and their proper course while at the mark (the "seamanlike" rounding you are thinking of). However, nothing prevents them from heading up and gybing to stbd.

When WP gybed, they had to give you room to keep clear (rule 15) - and you did

Rule 18.4 (Gybing) doesn't apply at a gate.

With WP on stbd tack, you were required to keep clear - and you did.

WP was still entitled to mark room (rule 18.2 c 1) - as long as they did not leave the zone.

No contact, so rule 14 doesn't apply.

No foul.

(this had to be really light air - no way could this scenario play out in a breeze)