I mean probably. In 1,000,000 such cases of devices causing injury in general, how many are caused by space particles and how many are caused by human fallibility? Whether it's a design issue, qa failure, supply chain issue with unexpected material in the device, or deliberate malice, the company is responsible for the product it sells, and the customer has a reasonable expectation that it won't explode.

The cosmic particle idea isn't completely outlandish, but it's impossible to prove, and it's statistically far more likely that it was a human failure. Given the rarity of spontaneously exploding batteries, I'd bet dollars to donuts that the particles are responsible for less than 1 in a million incidents, so yeah, the company should be liable. That's the cost of business, and on a humanistic note, making things better for the guy would just be the good thing to do.