The article being reported on does not make this conclusion. The study authors are interested only in the time it takes for (human) users to complete CAPTCHAs,

The article being reported on does not make this conclusion. The study authors are interested only in the time it takes for (human) users to complete CAPTCHAs, and did not examine the speed at which bots solve them. The fact that bots can solve them -- and solve them fast -- is apparently a well-established fact in the literature. There is a table in the article comparing its (human) participants' solve times to a number of previous studies which examined how fast/accurate bots can be. The Register (and the New Scientist, which most of this is cribbed from) is looking for a headline, so whatever. But the study's authors say that the "surprising" part is that "solving time and user perception are not always correlated" for human users. Game-based CAPTCHAs with sliders may take longer, but the users in the study still enjoyed them more than image-selection-based ones.