If it were a ceramic cap, it would have blown to pieces. A Thyrisistor is like a cap but more so; it is like a fuse but more so. On it's own it does not do much but in a grounded circuit, when its trigger voltage it hit (as in a spike), it sends everything straight to ground to protect the main circuitry from getting fried. Or so goes the theory; as everything else in life, they do fail with age and like a bullet proof vest, it can only be hit so many times before they fail or trigger.
