Strength, mobility and other non-running sessions
A plan is more than runs, and Runsei counts the rest of it. When your plan has a strength or mobility session and a matching activity arrives — strength training, HIIT, yoga, or the generic "workout" that stretching and flexibility often sync as — it completes that session automatically. A tagged ride or swim never does; those are their own kind of training and feed the picture separately.
What it assumes, and says out loud. Runsei can't see individual exercises, so a completed gym session is marked done on the understanding that you followed the programme — and the session says exactly that rather than implying it watched your sets.
How it counts. These sessions count towards your plan execution and your week, but never towards your running kilometres — turning a gym hour into distance would quietly corrupt every volume number you have.