I've read that apple seeds are poison but if your vet says okay, I wouldn't worry. I also read that acorns are poison and we actually fenced part of our yard because of it, but Bailey has eaten several and is okay. Who knows.
Apple seeds contain minute quanities of cyanide, but so do beans and many other vegies. The amount of apple seeds a person or a dog would need to eat to come to harm is very large.
No variety of acorn is posion as far as I know, many Native American cultures ate them as a main part of their diet, some are sweet like most nuts, some are bitter because they have a lot of tannic acid in them. This was removed by washing the gound acorn flour. Deer, turkeys and wild hogs feed a lot on acorns.