Mouse Finbar: Did I die and turn into a small muscular boy scout?
Dr Smolder Bravestone: Who is Jumanji?
Mouse Finbar: Is that Barbara's boy?
[Dr. Bravestone driving towards the flock of ostriches]
"Mouse" Finbar: What are you doing?
"Shelly" Oberon: Birds, birds, birds, birds! Birds!
[Dr. Bravestone turns around, driving towards the cliff.]
Oberon: What the hell, man!
Bravestone: They're flightless birds.
Ruby Roundhouse: This is a flightless dune buggy!
Milo Walker: What in the Sam Hill?
Young Marsha: I think he went back in. We gotta go get him.
Young Fridge: Are you crazy?!
Professor Shelly Oberon: No, no, no! I'm the old fat dude! This can't be happening.
Answer: He didn't die instantly because he didn't consume anything like Finbar did with the cake, his weakness to heat, sun, and sand is like the endurance he has and Finbar's strength and speed weakness it is simply a debuff on the character.