Resource guarding : when is it too much ?

Hi, I have a few questions about resource guarding and when it's appropriate or not.

I have a 1 y.o. male corgi (neutered). He's very friendly, loves everyone, everyone loves him. He never starts fights, but he hates when another dog comes too close when I'm feeding him/giving him water or playing tug. And by "too close", I mean, clearly intruding in his personal space.

He growls a bit and if it doesn't work, snaps at air to tell the other dog to get out and usually, the other dog gives him space, my dog shifts his focus back on me, gets his treat and goes back to play and there's no hard feelings.

When he does this when another owner is giving treats/water, that's when I step in and scold him.

My trainer and a few resources online say it's okay for dogs to guard their food/owner as long as there's no aggression. I've been told to not scold him for this. But sometimes, the other dog doesn't tolerate him snapping and escalates. They start fighting, we separate them and after a time out, they go back to play like nothing ever happened.

So my question is : should this "snapping at air" behavior be tolerated ? The escalation doesn't happen a lot. Maybe happened 10 times since I got him at 2 m.o.. but fights are always a bit scary. Should I book my trainer again about this ?

A few other things that might be relevant : he never growls or snaps at people who get near his food/toys/favorite humans. This mostly happens at the park (which is a big open area where dogs can avoid eachother, not your classic tiny dog park) but he also does the snapping at air thing indoors sometimes.

Thanks in advance, have a nice day.