I'm pretty sure planes are supposed to have a lock that prevents the door from opening at speed. If that wasn't the case not at plane, it could have failed. I don't know.

@TheFlightGuySP oh

The pressure inside the airplane is roughly equal to the ambient air pressure at/near ground level, so pressure won't be a big liming factor.

Oncoming airflow is a different story (as well as which way the door opens).
But the airspeed during landing isn't nearly as high as it is during cruising, and it's an outward opening door (which will get blown open depending on the direction of airflow).

I'm not an expert on the topic. These are just my assumptions.