I can't speak to BA procedures, but on a lot of airlines I've seen the crosscheck performed by the other cabin crew member on the opposite door. On 744/777 aircraft I believe the manual/automatic configuration of the door is visible from across the aisle. I've seen many times where the crew configuring the opposite door does a visual across the cabin to crosscheck.

At that time during the flight there's so much going on, it's entirely possible that his look was completely unrelated to the door config.