Wow, that is so cool! I had a similar time last year with wildflowers near my home. I started taking pictures just for fun, but then people living nearby pointed out spots I never saw. It became a shared map of all the best blooms in the area. There's a real joy in a personal project growing with help from others. Your sketch log turning into a group effort with joggers is exactly that kind of happy accident.
Honestly that sounds kind of annoying to me. Letting others into a personal project can ruin the quiet focus it started with. It stops being your own thing and turns into a group chore.