You need to get experience in judging divers before they dive. For those who have dived in varying locations and a variety of people it becomes somewhat second nature to be able to reasonably judge divers ability before the dive. A few checks on how they gear up, their reactions to the environment and others around them, all helps show how well they may dive. Its not an absolute but usually reasonably accurate.
I think I would find if someone came up to me and started telling me we are buddies and I have to do mask drills etc at the start of the dive my response may well be to go find another buddy as I have paid for a full dive, not go doing "proof of ability" dives. It would suggest to me that perhaps the buddy is nervous and somewhat inexperienced. I would however have the decency to chat with them and see what the issue is first, however if they were determined to go down that path to force me, regardless, then they would be doing it with someone else. Don't insult people by assuming all divers are dills unless proven otherwise to you, that's nearly as bad as assuming all divers are great.
I watch people when they prepare, even if they are not my buddy, not because I want to know everyone's experience as I am an "Expert, as I am NOT", but more because having travelled a fair bit and having lots of time to sit in airports killing time I people watch and one learns to judge people by doing this. After doing this with diving you soon learn to judge people by their actions and how they fit in.
As you said, his mask was tight, a sure sign something is not right. Fiddling with gear, inability to set up gear, clearly not geared up properly for the dive with gear missing are all signs that' all is not well (generally speaking).
A list to think about are;
Fiddling
Inability to set up gear
Appear lost with the process
Noisy and mouthy and done it all (covering their lack of self confidence)
Looking at everyone else for signs of what to do
Not at ease
Geared up fully and the boat hasn't left yet (yes seen this a number of times)
Gear clearly on wrong or not set up correctly
Been there when someone has shot for the surface in panic, only thing to do is what you did and others suggest, come up at a safe rate and be available if there is an issue. The guy I was with came up like a homing torpedo and was like a speed boat on the surface back to the boat, and was as calm as a cucumber when back on board, like nothing happened. He was a newly certified AOW and I believe panicked that we were going down to about 22m, particularly in open water.
Sometimes you will have your dive spoiled by an incident with an instant buddy. Sometimes such is life, as long as all are safe is the first consideration. You can always dive again, but if dead, last dive you will do. Having a dive spoiled sucks, but having an injury or death would be much worse.
Rule 1 dive safe yourself, rule 2 consider your buddy, rule 3 consider others. ALL IN THAT ORDER, as you cant save anyone if you are in trouble yourself.
