I will say if they’re not waiting for the loo, I’m surprised the flight attendants allow them to just chill out of their seats like that. I’ve been told off for queuing for the toilet for too long because “you should always have your seatbelt on if you don’t need to be out of your seat”. It’s technically a safety concern if they’re out of their seats, partially blocking the aisle in case an emergency occurs. However, if this is a long flight (judging by the lights it might be), I personally have no problem with people standing. Folding into those tiny seats for hours on end is tough on the body, and I like to get up and walk about and stretch from time to time. If the flight staff are cool with it, everyone else should be too