to have called this dog owner stupid

[WillowTit]

walking up the high street
young german shepherd, with whole family, with children, grandparent, and a man, dog not on a lead
my own ddog terrier would not like a german shepherd
a child tried to catch the dog, but failed
the man, shouted instructions at the dog
to think it is totally unnecessary and in fact bullying behaviour to the general public to let your german shepherd puppy go without a lead in this scenario,

It sounds absolutely ridiculous OP.

It should have been on a lead for the safety of the general public and other dogs and for its own safety - it could have run onto the road and been killed/ bitten someone and ended up having to be put down. Anything could have happened.

There are so many irresponsible and ignorant dog owners now.

There's a lot missing here. Was this GS showing signs of aggression? What was your Terrier doing? Dogs, being natural pack animals, will seek out the company of other dogs for play and dog play can be rough and look like a fight. The shouting sounds like it could have been an attempt to recall the GS.
Having said that, it is extremely irresponsible to have a young dog off a lead on a busy High Street - it's still finding out about the world and if it sees something that it finds interesting, it'll be off to satisfy it's curiosity.

Isn't it illegal to walk a dog off lead where there's a road? Pretty sure I've read that so YADNBU.

No, it's not illegal in the UK to have a dog off a lead anywhere unless there's one of these PSPOs ( Public Space Protection Orders) or a By Law in place telling dog owners they must do so. However, unless the dog is totally trustworthy not to suddenly decide to run across the road, I would say it's pretty stupid. Mine had a habit of trying to chase blue light vehicles, so she is never off lead near a road because I'm not sure she's got out of it.

Whilst it is stupid to have a dog off lead near a road, especially a puppy, I am not sure how it is "bullying behaviour". How does someone "bully" the general public?

How is it bullying? In case people are scared? I doubt very much that was the intention, using a puppy as a bullying mechanism! Not even a bredthats supposed to be muzzled/on a lead in public. I wouldn’t risk my lot off lead on a road, the sniffs are too strong and we have squirrels/pigeons/lots of crows.

What a total non-event.

Not sure why it’s bullying behaviour but it is stupidity, primarily for the safety of the puppy.