I love it when these chance occurances happen. Here is one of mine:
Indeed, that is a whole thread on exactly those types of events. In addition to the above, I have on occasion bumped into or spotted other unicyclists in Norway. Sometimes people I did not know but came to know latter on, including one of @PedalSprell’s old uni friends, Vidar (not on this forum AFAIK)
When I saw Vidar cycle past me for the first time I was having a coffee with someone who I did not know well and who did not know I was a unicyclist. However, I had turned up on a unicycle, much to my acquaintance’s surprise. While we sat outside the coffee shop chatting, Vidar cycled by. The person I sat with said, “Is unicycling a big thing then in Oslo these days?”. I replied “no”, then paused for a bit and said, “umm… I don’t think so, anyway!?”
Anyway, years later I met Vidar and pieced together it was him who cycled past that day. Indeed here is a photo of me with Vidar (he is in the middle, @PedalSprell is on the left and I am on the right).
I have also had chance encounters with @Erlend_Loe, though I did know him at the time. Indeed on one occasion I cycled up behind him and said some rude comment about how he must have lost a wheel. Because, you know… you have to, right!? 
And that brings my post back on topic because I was on a penny farthing at the time and hence a non (unicycle) rider… at least for that day. 