the sanda / muaythai connection

i am a wingchun practitioner, i have a little background in kicking but not much, not enough.... i saw a match between muaythai and sanda, but i didnt notice the difference between them in competition, sometimes the sanda guys would win, sometimes the thai guys would win.... i even competed in a sanshou competition once, but by then i was doing jkd, not sanda.... so i was wondering, how is muaythai training different from sanda training?