Barry, your last point is the key to it I think. Humphrey‘s pretty sociable, we‘re in a club and he gets plenty of opportunities to interact with all sorts but every now and again there‘ll be a bit of a commotion, particularly with newcomers as he seems to decide its his job to give them the once over before deciding if they can join. However, while most are tearing around chasing each other, he‘s happy to plod along, on his own, nose down catching up on the news!
Reading the body language isn‘t always so easy, and I read an an article recently suggesting that even the dogs have problems reading a different breed, a french bulldog with no tail, a creased face and a particular stance doesn‘t have the same accesories (for want of a better word 😉) as lets say a German Shepherd, so its feasible that misunderstandings do occur and it would also explain why some breeds might be labled trouble makers when perhaps they‘re just having problems communicating what they‘re feeling. Its an interesting theory and would explain your pug incident!
In answer to the original post, I agree with Pearly and if you have a good recall and he‘s not showing any other signs of agression, I wouldn‘t worry too much. Humphrey‘s still entire so I‘m always aware that there‘s potential for conflict with other new males but given enough space and initial distraction, most incidents can be diffused before they become serious.