deangelr is a very experience clownfish breeder and anemone expert. He said it is caught, then I am sure it was caught.
Clowns are not like other fish and do have some defenses against anemones which we are not fully understand. That was likely what save the clown. Clown or not, if he get a full dose of the stings, he is likely not going to live. I think being a clown fish, the anemone maybe confused as to he is actually food or not. The anemone likely not fully stung him so he was able to excape.