TL;DR: this is simply not true in practice

To be at risk of cyanide poisoning from apple seeds, you would need to consume a significant amount of crushed seeds, with estimates ranging from 150 to several thousand. The exact number depends on the apple variety. Apple seeds contain amygdalin, a compound that can release cyanide. The cyanide content is around 700 milligrams of hydrogen cyanide per apple seed. A lethal dose of cyanide is approximately 50-300 milligrams. Therefore, you would have to eat roughly 1,000 apple seeds to reach a lethal dose. Some calculations suggest that consuming slightly more than 250,000 seeds would be fatal. Eating 29-38 apple cores, assuming each apple has 6-8 seeds, could cause serious harm. You'd have to eat upwards of 20 apples in one sitting and chew all the seeds to be affected.