As a guy, I can see how the woman in the Guardian article was not happy about being slipstreamed by a stranger. The setting matters, of course. A big charity ride in a larger mixed group may give more opportunities to strike up conversations with random strangers. But on an isolated section of road an athlete doing a training session doesn't want to socialize or pull some recreational wheel sucker around.
My experience is most folks out exercising solo are not out to socialize. Runners are literally in their own world with their earbuds. Cyclists like me have specific goals (route, duration, intensity) for a training session, and I'm not going to throw that plan out just because another cyclist crosses my path. Usually a short greeting/wave/nod are sufficient. If stopped at an intersection for a minute you can compliment someone's bike and chat, but then wish each other a good ride and be on your way.
Also, as a middle aged guy, it's good to remember that I'm rather invisible to younger women. So if I were to say something other than "good day" in passing it would be like a ghost had materialized in front of them. Of course they would be startled.
