Translation:The eighty-eighth cook does not cook, but he eats lunch.
I wrote "...but he has lunch" it was rejected and the correction was " but he's lunch". Is it normal?
Not normal - and not right. You can only say "he's lunch" if he is being eaten - not doing the eating!
The issue is that if "have" or "has" is the only verb in your clause, you can't contract it. The verb is stressed in those cases and it needs its own syllable.
- He has got a cat. - He's got a cat.
- He has eaten lunch. - He's eaten lunch.
- He has lunch. -
He is having his lunch was rejected but this seems to have been covered already
No, this one has become extremely picky about what it will accept. I put the 88th cook is not cooking but he is eating his lunch. It wouldn't even accept "not cooking."