It's a typo, there's no way a 255 would be 100% safe on an 8" rim and you'd have the devil of a job blowing it out and getting it seated onto the bead.
Everyone else's 255/85 fitting charts use 6.5-7.5" rims with 7" being the measuring rim. I ran two sets of BFG's in that size before the 762's.
I think I mentioned it to my tyre bloke who told TyreMax but they were too dumb to do anything in their new catalogues.

