Past Progressive vs Imperfect
Hola,
Yo sé que se dice
Él llamó cuándo yo comía
pero suena bien decir
¿Él llamó cuándo yo estaba comiendo?
Corriga mi español por favor 
Gracias
2 Answers
It is my understanding that the imperfect is generally used in Spanish in this type of situation even though we would use the past progressive in English. Only if you really wanted to emphasize the ongoing nature of the event would you use the past progressive.
An example of the latter might be: He finally called me after I had been waiting for three hours. Here, to emphasize the lengthiness of the wait you should use the past progressive with llevar + gerund instead of haber/estado/gerund. Another example: I finished the job by working non-stop all day long. Here you emphasize the long lasting difficulty of the effort by using the past progressive.
Finalmente me llamó después de que llevaba tres horas esperándolo.
Terminé el trabajo trabajando sin parar durante todo el día.
Notice in the last sentence you do not say POR trabajando. The "by" or "while" that occurs in such sentences is translated by just using the Spanish gerundio by itself.
My non-native opinion:
Él llamó cuándo yo comía is like: He called while I was eating.
¿Él llamó cuándo yo estaba comiendo? Is like: He called while I was in the middle of eating.
The switch from comía to estaba comiendo emphasizes the ongoing action and hence accentuates the interruption of the activity. The same why I did in English by putting in the middle of.
(I don’t see any obvious errors in your Spanish)
Await other input.
