YADNBU - I had a similar albeit more polite version when I was heavily pregnant and walking with my 2 year old to nursery.
Now, I am scared of dogs. I used to be properly phobic but I have worked hard to overcome it and now I would say I am cautious around dogs but no longer fully terrified. The reasons behind my phobia are likely many but it was fuelled by 2 dog related incidents when I was a child, one involving a Doberman when I was about 5 and one involving 2 German Shepherds when I was about 10. In the latter incident I ended up being bitten on the leg.
ANYHOO, my point is that no one just walking along with their dog knows any of this. So when a young off lead German Shepherd was running towards me down the pavement and I was encumbered by a very pregnant belly and a toddler I found it absolutely terrifying. This was on the pavement by the side of a relatively busy road - not off in the woods.
The dog was, it turns out, very well trained and the owner just whistled and he turned without breaking stride and returned to him. But I did ask the owner why he doesn’t please use a lead and he said - much like the bloke you spoke to - “if I needed a lead I would use one”
I have since seen them walking around quite a lot, never with a lead and, to be fair, the dog is always under control, but to someone like me it literally feels like seeing an enormous man eating tiger wandering down the road next to me and my toddler. And I’m trusting in the training of a stranger and the unpredictable nature of a dog I don’t know that nothing bad will happen.
Is that irrational? Yes, probably my fear is still irrational and I get that the man has probably put in lots of time and effort training his dog. But, I still think people should come first and that means dogs should be on the lead when on a road!
Sorry for the essay - but I think it’s important for people to understand how it can feel to see a dog off lead (and obviously it’s different in a field or dog park or something).