From EVA's own site 'Earning Miles on Star Alliance Partners - Mileage Table'

AVIANCA (Travel date after 2017/10/12) Business C/D/J/A/K Actual miles x 125%

So avianca's K is business, here I second qupasyd's opinion, we are talking about avianca's not EVA's K booking class.
Actually I've made two phone calls to EVA (trying to select seats), both representatives stated clearly that I booked business seats, so I am not worried.

One annoying problem is about seat selection. Avianca told me to contact directly with EVA for it, and EVA said avianca has to send a request first. So neither of them wants to help assigning my seats. Well, I guess it's a common phenomenon for codeshare booking.