The fact that the people who perform best in interviews aren't also the people who perform best on the job doesn't invalidate meritocracy; it simply means that interview environment/tasks are a poor approximation of job environment/tasks. Non-meritocracy would mean that you don't choose the people who interview the best, but instead choose people you (1) like most, or (2) have a particular skin color, or (3) have perticular interests, etc.

The second part of your comment is less relevant, as I think most "tech" people would say that e.g. promotions (management), product development (marketing) and the general market dynamics are highly "non-tech". But in many of these areas, people do try to choose the best - at least as far as marketing is concerned, companies dislike wasting money and choose to promote those people/products that they expect will produce the most profit. Companies' "profit", of course, doesn't correspond to a person's "merit" ("profitcracy"?), but the basic mechanism is the same.