what is the diff between towing cap & 5th wheel towing cap

There is likely a typo on the rating.

But 5th wheels do generally get a different tow rating but it's usually higher and not typically a 50% difference.

For example: We have a 2008 F250 Crew Cab Short Bed V10 4.10 rear end.
- Conventional Towing 12,500
- 5th Wheel Towing 14,500