It's in the computer?

Yeah, basically. lime's summary was rather curt, but basically accurate. He explains his intent really well in the interview I linked above, or I assume you can find his writing or text-based interviews somewhere online. Here's a mostly-good summary of the idea in a review of his book on the topic:

A centaur, in automation theory, is someone assisted by a machine, whether using a hearing aid or driving a car. A reverse centaur is someone whose freedom is diminished by the demands of a machine, like an Amazon warehouse worker. The technology of AI theoretically allows every worker to be a centaur, but the business model demands the reverse. Take radiology. In the centaur scenario, a human radiologist works with an AI radiologist to produce more accurate analysis, but that costs the hospital money. In the reverse centaur version, the AI radiologist demotes the surviving humans to the level of results-checking drones who are more likely to make mistakes. Much cheaper, but you see the problem.

In the centaur scenario, the human radiologist is basically doing their job as they do now, but occasionally the AI might pop in and say "hey, check that one a bit closer". It helps them find possible errors they've made. The reverse centaur reduces the human's job to in theory validating the AI's results, but because of a phenomenon called "cognitive surrender"—which has been talked about since before AI but has become very popular over the last year or two—they end up just ticking "yes". Think Homer Simpson in that episode where he works from home and uses a drinking bird toy to just press "y". The human is providing the "leg work", so to speak, for the AI's thinking.

(and before anyone comments on it. alt+0151. I've been using em dashes regularly since like 2009, and I refuse to let AI steal that from me.)

you do the manual labour while the computer makes the decisions.

The computer is the horse