Here's a breakdown of why:
* "Mittel" means "middle" or "average" in German.
* "Gruss" means "greeting" in German.
Combining them wouldn't make sense in standard German.
Possible interpretations:
* Typo: Perhaps you meant "Mittagsgruss," which translates to "afternoon greeting."
* Informal slang: It's possible that "Mittelgruss" is a regional slang term or a humorous invention.
To clarify what you mean, please provide more context or the original source where you encountered this word.