My dad got into an serious accident in hius Lexus 300 ES (2000) and his air bag deployed. Is the seatbelt supposed to lock him in? The police seem to think so.

My dad got into an serious accident in hius Lexus 300 ES (2000) and his air bag deployed. When the police arrived, they insisted that because my dad was able to get out of the car, he must not have had his seatbelt on (which he did otherwise the car would continue to beep). The police officer insisted that the lexus seatbelts are designed to lock in place in a collision, so someone else would have had to let my dad out. This sounds a bit crazy that a lexus would lock the driver's belt in the case of a collision. Can you please help clarify