They powered up the centre engine, then lit two engines either side of it, but then turned those off a few seconds before landing and still actually landed on a single engine for the last ten seconds or so. It’s hard to be sure exactly because the telephoto footage of the booster catches the start of the burns but misses the side engines shutting down. But when it pans back on to the engines, it’s clear only one of them is still lit (with one other flaring off some unspent fuel). That’s a very precise and tuneable thrust curve you wouldn’t be able to do with one bigger engine.
Interesting about the final part of the landing occurring with a single engine even with a 3 engine landing. Makes me wonder why they don't do something like 9 engines for the breaking burn and then switch to a single engine for the landing part. It might just be that is their final plan but 3 is easier to test than 9.
This 3 engine landing failed for the centre core, which is why it was lost. Specifically, there wasn't enough 'lighter fluid' to relight all 3 engines required, only one engine was lit. Thus the booster tried a 3-engine landing on a single engine, and hit the water at 300mph IIRC.