Problem could be with the kick starter quadrant jamming on the ratchet.
Happens occasionally if there is wear in any or all of the following:
- quadrant teeth
- ratchet pinion (teeth)
- kickstarter shaft bush (in outer cover)
- brass bush which ratchet pinion turns on.
If it occurs again, it is easy to prove; put bike in gear and rock forward; this will re-position the quadrant and it will kick over.
Richard