While we're guessing, I would guess that they use a high quality Grade 8 pin for testing or better as they want to isolate the point of failure to the item being tested.
That said, you bring up a great point. I highly recommend that everyone reading this verify the rating of the type of hitch pin they have BEFORE using something like the Factor 55 Hitchlink as a recovery point.
From Factor 55's site:
- Never exceed factory receiver hitch pull rating
- Always use a quality steel alloy 5/8” hitch pin
- Always pull in line with the hitch, do not bind or side load the shackle
Some would argue that Grade 5 is better suited for shearing forces than Grade 8. Here is a Factor55 HitchLink 2.5 and Grade 5 hitch pin for recovery use (the 5/8 Master Lock is for bike rack security).