I saw a post where the poster just ad the tags for the artist, character, copyright and one general tag. and the general tag is just "c"

Does this meet the requirements of the "four tags" rule?

Sorry if my grammar is off. I used google as help.

four tags is four tags no matter what tag type they are. though im p sure that c is not a valid tag and doesnt count

Yes. They are considered some of the more important tags, especially artist since sometimes it is unknown who made it.
The only tags that do not count as tags is tagme, invalid tag, junk/joke tags(eg: tag it yourself, which unfortunately was a tag someone used), and meta tags(eg: rating:s, rating:e, source:example.com, etc).

Why is "c" a tag?

NotMeNotYou said:
Why is "c" a tag?

Because “C” is the name of a character by Crepix.

UltCharger said:
Because “C” is the name of a character by Crepix.

that probably should be c_(crepix) and not just c