Honestly, it sounds like a pretty normal reaction to me, given the situation. Big groups of dogs can be very intimidating, and for a dog that may have confidence issues I don't think his reaction was abnormal at all.
We sometimes see a few older people walking a 'pack' of Springers, all off lead. Being Springers, they dart around doing their own thing and not paying a blind bit of attention to their owners. They are actually a real pain in the arse -- chasing my dogs while barking and trying to nip, like a sheepdog. The owners think that the dogs are playing, but what they are actually doing is asserting themselves and being rude because they are allowed to get away with it.
My point is, dogs can be very subtle when it comes to body language. You may not have realized it, but one or more of the dogs could have been displaying unfriendly body language which spurred Alfie into 'defensive insecurity' mode. Equally, it could be that all of the dogs were displaying perfectly friendly body language and he felt overwhelmed and pushed him into reacting. Either way, I wouldn't be concerned. After any incidents with other dogs, their confidence can really be knocked. If you slowly build it back up (which should happen naturally with time) eventually you will find that he will probably stop acting in that way.
We sometimes see a few older people walking a 'pack' of Springers, all off lead. Being Springers, they dart around doing their own thing and not paying a blind bit of attention to their owners. They are actually a real pain in the arse -- chasing my dogs while barking and trying to nip, like a sheepdog. The owners think that the dogs are playing, but what they are actually doing is asserting themselves and being rude because they are allowed to get away with it.
My point is, dogs can be very subtle when it comes to body language. You may not have realized it, but one or more of the dogs could have been displaying unfriendly body language which spurred Alfie into 'defensive insecurity' mode. Equally, it could be that all of the dogs were displaying perfectly friendly body language and he felt overwhelmed and pushed him into reacting. Either way, I wouldn't be concerned. After any incidents with other dogs, their confidence can really be knocked. If you slowly build it back up (which should happen naturally with time) eventually you will find that he will probably stop acting in that way.