No, Sanya, you are right: it should be "he lost his job." He struck his boss, so he was fired; fired = lost his job.

Yes, it is necessary. The sentence does not say "He lost his job". He was lost in his job. He was lost in the big house. He was lost in the forest. He was in a strange job which he didn't understand, so he was lost.

Thank you Brad C for your help.

Or maybe it means that, because he hit the boss, he couldn't change jobs, and so he was "lost in" the job he has now at the fertilizer works. Meaning he was trapped there, with no hope of changing jobs and finding something better. If I were writing this sentence, however, I would say "trapped" rather than "lost." It's very unclear (as all these different answers show!).

Then I repeat my earlier answer below!