Could be missing it in list but pretty sure the issue is that city has not been imported into Citystrides before. You can search imported cities here. I found a couple of other Cornwalls in Canada but not the one it looks like you ran in.
When a city is missing in CityStrides, it needs to be added to a spreadsheet (How to help with missing/broken cities/regions) for James to review if it’s possible to import from OSM. It looks like someone has added it to the spreadsheet recently so nothing else to do on your part.