I've heard of it too, but with farmers sitting in a tractor cab at 62f all day in a t-shirt and then coming out into 94F with high humidity? Or maybe they had a bad egg salad sandwich for lunch and it caught up to them at 4pm? Getting in and out of truck a dozen times an hour should be fine.
The swimming thing is real though, I wasn't there, but a close friend in high school drowned from a big lunch and then deciding to swim out to an island with another buddy, he got cramps, I guess panicked and drowned. Or maybe there was too much chop to float on his back, or he didn't know to do that, but he drowned.... Any serious exercise will give you cramps after a meal, I've done than before, so I don't go for a swim after eating, but floating around in the pool is fine...