They didn't sack him, he quit for better pay.

In Japan companies rarely sack employees and employees rarely quit. People are expected to stay with the same company basically their whole life. That's why he didn't get fired for disobeying orders. Firing someone in Japan is somewhat socially taboo (just like quitting) and therefore rare.

In Japan, companies are considered to be like "family". It would be kind of a joke here in the USA, but in Japan there is a lot of loyalty in both directions.

Part of the reason they sued him is probably the butthurt of him quitting. Quitting, even for better pay, is kind of like a big "fuck you" in Japan.