Accidentally put transmission fluid in my engine

you need to quit driving the car NOW. Transmission fluid is non-lubricating. Flushing isn't necessary though. As for the "old days" we were lucky to get 100k out our cars back then too. Could be a coincidence?

ATF is glycol based. Yes, there are many oils used in ATF under careful and exact chemistry. Oil is oil based. (fancy that). Either can be synthetic. Oil lubricates under very extreme conditions. ATF is meant to transmute power within the liquid. It cannot hold up to extreme temperatures. Mainly, when two dissimilar liquids are used in an engine or piece of equipment, they cannot and will not mix. Little air bubbles are produced. The air bubbles provide no lubrication. Therefore, it's like running your engine with no oil at all. The same thing happens if you run two different types of oil, and sometimes (rarely) even if you run two different brands. Change your oil immediately. Don't run the engine until you do.

Do not listen to anyone who says its ok or dont run it long and change the oil asap. Trans fluid will destroy your rear and front seals. At first it swells them but in a period of about and hour or two after running it the rubber in the seals will become mushy and within a day or two youll be missing oil as it begins to leak from the front and rear seal. As an example find a piece of rubber and put ATF on it and check it the next day. The rubber will fall apart in your hands. Rubber and ATF never go together.