That's the only test the guy did when he came; he didn't look at the cooker or do any tests on it.
There's a clue that he wasn't too bothered about what's really wrong.
It could be a bad element on the oven, or it could even be a neutral-to-earth short somewhere in the unit or wiring (this can lead to all sorts of apparently random tripping, depending upon what else is turned on at the time).
I'd suggest that you get somebody else out to check it over.
