Not to sound negative, but I'm not sure that means much tbh. Plenty of times players after doing an ACL people feel ok after the initial pain. He was in quite a bit of pain early but seemed ok later, which is pretty standard. Not suggesting that's what he has done, just that him saying he doesn't think it's serious doesn't really change anything.
They do conduct a number of lateral movement tests in the rooms immediately after and generally a competent medico team can ascertain if an ACL has been ruptured.
Fingers crossed for Bam.