In my experience some dogs don't like puppies! My Paisley is one of these dogs. She WILL NOT tolerate their silly paws in the face clumsy behaviour and will tell them in no uncertain terms that she is not happy! She gives them the growl, then the lip curl first and if they don't get the message to back off then she goes in for a teeth snappy nip. IMO this is perfectly acceptable behaviour as she has warned them off in a polite way but they have ignored her. How else is a puppy to learn the correct way to say hello if they're not told off when they are OTT!?
Did Hector give his warnings to the pups before lunging at them? If he did then I wouldn't worry too much. Sounds like he has just matured out of puppyhood and doesn't want to be messed about with by silly baby dogs!
However, if he seems to be sensitive around meeting dogs and doesn't give much warning, perhaps he has hurt himself and is making sure nobody gets too close as he is in pain?