Ascarid means roundworms, so Jackson should be covered
He would have had to ingest the puppy's poop, eaten soil or grass that the puppy had recently pooped on, licked the puppies butt (lol, but we know dogs do this) or walked through an area that the puppy pooped at and then licked his paws.
Because of the heartworm rx, I'd say Jackson was well protected, but if you want to be 100% sure, have your vet check his stool sample in a few days and then again in about 2 weeks. I wouldn't use a dewormer since he's on that rx which may have the same active ingredient that would be in a dewormer.