[Edited to fix: date of refrigerator comment upper bounded by 1953, not in 1953]. So it's possible he formed the opinion pre-freon, but it seems more likely that it was during the Freon era.
Ammonia and other nasty chemicals remained in use well after then. For example, apparently GE sold their Monitor Top-style fridges with sulphur dioxide or methyl formate as the refrigerant until at least 1936 and they stayed in use for decades after they were discontinued.
My parents had one of those and used it until the early 2000's as their "garage beer fridge". They sold it for a substantial amount to a collector when they moved. Dad was a chemical engineer and I'm not sure he knew how toxic the refrigerant it contained was - he probably would have gotten rid of it sooner if he'd known.
To be fair CFCs are toxic to humans, but only once they escape to the upper atmosphere to decrease the LD50 of sunlight. Of course in 1953, there was no way Erdos could have known that.
Ugh I meant Godel. All of these mathematicians get me confused. Because of his incompleteness theorem, I'll have to leave your other question unanswered.
Freon was invented in 1928, and started mass production a few years later: https://en.wikipedia.org/wiki/Freon
By 1935, 8 million refrigerators had been sold using Freon as their refrigerant: https://www.thoughtco.com/history-of-freon-4072212
His refrigerator comment was some time before 1953: https://plus.maths.org/content/goumldel-and-limits-logic though another source places it around Einstein's death in 1955:[1]
... ahhh, the wiki hole is deep today. :)
[Edited to fix: date of refrigerator comment upper bounded by 1953, not in 1953]. So it's possible he formed the opinion pre-freon, but it seems more likely that it was during the Freon era.
[1] https://books.google.com/books?id=iWy1AAAAQBAJ&pg=PA332&lpg=...