Any chance they saw you earlier and moved into single file to let you pass?
They would have had to have spotted me before I spotted them, which would have been at least a minute earlier.
I smiled and say hello to various other people who did step aside, hold their dogs out of my way, or who smiled at me.
This couple seemed to be engrossed in conversation when I caught up with them so it would have seemed rude to talk over them.
I was surprised when the man broke out of his chat to be snarky to me. It isn't a big deal, but I didn't like the feeling that he probably spent the next 5 minutes moaning about 'bloody cyclists'!
Before anyone mentions bells... Years ago, after several walkers suggested that I should get one, I did. I then discovered that about 1/3 of people like them, 1/3 are so deaf or distracted that they don't hear them, and 1/3 find them annoying. One person didn't react to the bell so I used it again. He then said that he was not going to jump every time some idiot on a bike rang a bell. Furthermore, if I rang it at him again he would tear it off my bike and stick it up where the sun doesn't shine!!!
I don't bother with bells now. If I have to, I just cough at a distance to alert the walker, or call out a polite request to let me through.