What you choose to count is up to you, but I find that it's not nearly so clear-cut when a movie or single is released late in one calendar year and sees most of its action the following. This is often recognized in retrospectives of the era...e.g., CNN's 1968 series and TIME's 1968 special issue covered The Graduate as a de facto 1968 film because most of its theater run was in that year.
CNN would be incorrect (not uncommon for that channel). When a film is planned for release at a certain time, it simply means it is one of the movies of that year. A settled release date is not fluid where December of one year randomly becomes January-forward of the following year, hence the reason Superman II is a 1980 film, or Star Trek - The Motion Picture (released 12/7/1979) was and will ever be accurately categorized as one of the films of 1979.
The point focused on McQueen being far above contemporaries in 1968 as a point in the review of The Thomas Crown Affair; you posted a list of stars who made more money than McQueen (which was not the point of noting his status in 1968), but each star's film earned less than McQueen's in the year in question. In fact, in Eastwood's case, his biggest film that year--Where Eagles Dare--was not really an Eastwood film, but an on-request, Alistair MacLean-penned vehicle for Richard Burton, so Eastwood cannot receive full credit for the film being "his", while John Wayne's biggest earner still fell short of Bullitt, which means the original point:
McQueen at the height of his popularity. There was not another star anywhere near that level in 1968.
...stands.