It's intended to be read as
non-(community wiki)
rather than:
(non-community) wiki
That is, "non-community wiki" (in this context) means posts that aren't community wiki, rather than posts that are wiki in some way other than being community wiki.
You might want to submit a bug post on Meta.SO requesting the wording be changed, if you believe it's confusing. I wouldn't recommend changing "non-community wiki" to "non community wiki" or "non community-wiki," but I would suggest a rewording to something like this:
Earned at least 100 total score for at least 20 answers (except community wiki) in the (tag name) tag
Or this:
Earned at least 100 total score for at least 20 answers (that are not community wiki) in the (tag name) tag
Or:
Earned at least 100 total score for at least 20 answers (other than community wiki) in the (tag name) tag
When similar opportunities for confusion arise on meta, I usually use the less formal "CW" as an abbreviation for community wiki. While "non-community wiki" is confusing because intuitively dashes have higher precedence than spaces, "non-CW" remains unambiguous.
That might also be suggested as an alternative wording for the badge description. But "CW" might confuse people who don't know it stands for "community wiki."