Instant mixes dont use the Audiomuse backend:
Those mixes are created based on the artists genres then are passed to the personal mix generator. When starting an instant mix from an artist, that artist is ensured to be seen relatively frequently in the mix.
Symfonium only use Audiomuse for track queue (Sonic Analysis) and the other Smart queue options. 
You can also see on what basis the track is added by viewing the queue. If it has one of these symbols beside it like this it has been queued using the Audiomuse backend:
