During GPS track post-processing, if part of a GPS track:
- goes “off the map” rather than following an existing road
- is characterized by short segments and abrupt angles, rather than long straight stretches
- totals less than a certain distance
- never exceeds a certain speed
- returns to its starting point before resuming driving-like motion
then it probably represents walking rather than driving. Adjust these heuristics and you probably could identify bicycling as well.
The point is not to make Waze a walking app; it is to protect the road statistics from the “pollution” resulting from leaving the app running while walking, without depending on Wazers to remember to turn off the app or set an appropriate mode.