It wasn't wet paint.

 I do however think the weight on the dried paint compromised it.  There's no way the tensile strength is appropriate for vehicles like The Beast.

 Also Trump claimed a knife could not cut the lining, and now claims a knife cut the lining.

Looks pretty wet to me

 Water on dry paint is not equal to wet paint.  For instance when we see a sigh labeled "Wet paint" we do not typically assume it is dry paint that was later covered in moisture.

 The shiny square does not appear "wet" by definition to me as the wheels do not collect any pigment.  If anything they left dirt behind.  This of course does not mean the lining was not damaged.

 The Beast by the way is the POTUS limo.  Pretty amazing machine, I've seen it a few times.