This was his suit from the Mercury flight - a suborbital 15 minute flight in 1961 that traveled only some 300 miles down range.
The Apollo program used an entirely different kind of equipment. The fire was in 1967, 5 and 1/2 years after the suit in question was used.
If anything, the suit would have shown the effects of immersion in water. Grissom's flight was the one where the hatch blew before it was supposed to, the capsule sank, and Grissom almost drowned.
thanks for the explanation.