Hi, imany :) .
First let me state I am not a qualified teacher.
If I am treading on any toes here please say so and I will bow out gracefuly.
You are correct with your knowledge of when to use the first three examples.
Your last example is used when you were eating an apple whilst something else was happening. e.g.
I was eating an apple when I saw a large green worm crawl over my fingers.
During class I was eating an apple when the teacher threw a large piece of wood at me (chair) to show his displeasure at my actions.
The term you use - is this mean - should read....does this mean.
Hope this helps .