It is annoying when I create a running segment and the top ten "runners" have average mile paces around 3:30. I would like to reject these people as segment leaders
Agreed! I have also commented on Motorcycles on cycle segment boards. There are however, three issues here I think. Firstly, there is one purely for Garmin when correctly identified activities appear in the segments for a different activity. Secondly there is the issue of people incorrectly identifying their activity (either deliberately or accidentally) and thirdly there is the problem of users forgetting to switch off their devices and so tracking their car journey home as part of the activity.
If segments are not to become excessively frustrating for users, Garmin needs to find solutions to these problems.