Why this meaning is not correct?
"My nephew does not eat sandwiche with egg."
Totally agree with you.
It seems to me like "My nephew is not eating an egg sandwich" could be a legitimate translation of this sentence. Am I wrong? I've reported it, just in case.
I think "egg sandwich" describe a sandwich with only egg (and, obviously bread). And "sandwich with egg" If there are more ingredients. For me both of they're correct