Tires are cupped. Bad struts or bad alignment?

Brought my Honda Accord 6 months ago. Passenger side rear wheel had hit a curb(before I brought it) and blew the strut.

The cheap dealer only replaced the passenger side rear strut to "make things right". 6 months later(now) I'm looking at my tires and I'm noticing minor cupping on the inside edge of the DRIVER side rear wheel(side with original strut that wasn't replaced).

I read that it could possibly be alignment that is causing the cupping, or it could be the strut. How do I find out for sure if it's alignment and not strut/vise versa?

Tires are Yokohama Avid Envigors. Car has 45,000 miles. I don't notice any major toe/camber issues with the wheels.

Cupping is usually caused by bad strut. But it can also be caused by tire/wheel imbalance. Struts have a useful life of 50,000-80,000 miles depending on road conditions. Sounds like yours was abused. Read this post on struts

Something is bent yet. If it's just an adjustment both rear tires would be worn. An alignment machine will point out what's bent to a good alignment guy.