technically a full sentence must contain a subject and a predicate (a noun and a verb). the full sentence version of your example would be:
"there is a big difference between the two."
"there is a big difference between what two?"
"there is a big difference between your man and the average man."
Only so much as women say "my man" in English when referring specifically to their husband... which in my mind is a tad derogatory. Formally, "husband" in French is « mari », and "wife" is « femme ». « Ton homme » in this phrase could mean husband, but it could just as equally mean boyfriend or fiancé as well. It's a tad generic for my liking, but that's Duolingo sometimes...
I translated "moyen" as middle, as in "les moyen ages" = "the middle ages". It still makes sense with the translation "your husband is the middle man" if he's the go-between or intermediary between two people. Is there another name for this kind of person, or would "l'homme moyen" work?
I think that "moyen" means "average" (literal meaning) when placed after a noun (like in this exercise), but when placed before a noun, it means "middle" (figurative meaning). This is very similar to several other adjectives, which can change their meanings, depending where they are placed.
just think of it as like in math. If moyen equals to middle, in math, what is the middle of 8 and 9? OR what is the average of 8 and 9? but I`m not sure if moyen is also used with numbers so far as math is concerned in french...but it makes sense to use moyen as middle...je pense...
First off, it would be "your husband" not "your man." Additionally, while that could be something you might say if you had the right context, it's too ambiguous to work as a correct translation of what is a much more specific sentence. Your sentence could be a response to "What do you think of my husband's painting skill?" "Your husband is average." That's something different from saying "Your husband is the average man."
You have to picture a taller/larger man on one side, a shorter/smaller man on the other side, and an average/medium man in the middle. The speaker is referring to the man in the middle.
Another way to consider this is as a generic noun; "an" average man. In this sense, the speaker is calling the man normal or ordinary, as compared to other men.
But for the record, no anglophone would speak that English phrase in the intended context. The sarcastic humour in some of the above comments reflects this, as calling someone "average" or "ordinary" can be taken as an insult. Perhaps in French, the phrase simply serves as a means of identification.