Q: Apparently faulty fuel caused cambelt to slip and ruin valves

I bought a car and 6 weeks later, I was driving along and the vehicle started to lose power and the engine warning light came on. I pulled over to the layby just ahead and turned the engine off and googled what the light meant, seeing on the RAC website that you shouldn't drive around on the issue, not that I could anyway, I called my father to tow me home.

The company I purchased the car from are claiming that contaminated fuel purchased 6 miles before the issue occurred has caused the engine to miss fire, thus causing the timing belt to slip, thus causing damage to the engine valves and a full engine replacement being required.

Could you please advise if contaminated fuel could cause this extent of damage, and if so, how would you know the fuel was contaminated to cause it?

My car has 72000 miles.
My car has a manual transmission.