I was reading the rule reference 1.5 and found out that "Counterpart: Unit Name" is a keyword type of "counterpart keyword".

I was immediately confused, cause as far as I know, "unit" and "weapons" are the only two types of keyword.

Naturally I looked "keyword" entry and it says, "There are two types of keywords: unit keywords and weapon keyword."

So... which one is right? Are there new, third type of keyword and they forgot to add it? Or it's just a typo on the "Counterpart" entry?

I don’t think it’s saying the keyword type. I think it’s just clarifying that the entry if for the counterpart keyword, not the counterpart card or some other type of entry.

Yep. Probably getting us ready for an upcoming release

Probably for a C-3po/R2 unit where one has the unit card and the other has to be included in the previous unit.