Yes, of course there are accidents from other manufacturers' rides but that's 10 incidents from 9 different manufacterers and I wouldn't really class stranded riders as an accident. Even the ones that are accidents are mostly very minor.Let's see.
1. Fujin Raijin II is a Togo coaster. Not Intamin. (one dead, 19 injured)
2. Steel Dragon 2000 is a Morgan coaster. Not Intamin. (wheel assembly falls off, coaster derails, injures 2)
3. Wild Thing is a Morgan coaster. Not Intamin. (coaster derails, injures 14)
4. Batman & Robin: The Chiller is a Premier Rides coaster. Not Intamin. (wheel assembly falls off, all Premier launched coasters shut down)
5. Raging Wolf Bobs is a Dinn Manufacturing coaster. Not Intamin. (coaster derailed)
6. Timber Tower is a Huss ride. Not Intamin. (riders stranded for 6 hours)
7. Magnum XL-200 is an Arrow coaster. Not Intamin. (bumping trains)
8. Enterprise is manufactured by Huss. Not Intamin. (ride fire)
9. BORG Assimilator is a Vekoma coaster. Not Intamin. (seats unlocked while ride was in motion)
10. Son of Beast isn't an Intamin. (structure breaks, injuring 27)
I only listed the events I'm aware of off the top of my head. So, there are PLENTY of accidents that happen on non-Intamin rides
Just look at the recent accidents on Intamin rides in comparison
1) Lapbar failure on Hydro(1 death)
2) Simular incident with Perilous plunge - don't think that this was fatal though
3) Superman Ride of steel lapbar failure (1 death)
4) Lapbar failure on Journey to Atlantis (1 death)
5) Cable snapping on TTD (front few cars injured)
And now the Superman Power of Tower incident too. You have to say that the proportion of major Intamin acciedents to other manufactures is quite worrying