So, it seems Thrash and Outrage work differently, for some reason. Could both you, Level 51 and Tase test both moves again in Link Battles?
I tested Petal Dance against a Sap Sipper (who was already in play, not switching in) and Petal Dance did indeed cancel. Afterwards I realized it would probably be worthwhile to test all three moves each in two scenarios (already in play vs. switching in), and I also didn't think to save the video of my battle. It's really late now, but if someone hasn't done all this by tomorrow then I'll be glad to test it all then.