Not near drums right now to test, but I think that makes sense and might be a good idea (Especially if he’s saying it).
Small, lightweight splash cymbals don’t have as much rebound as the normal drum and ride cymbal surfaces that we give most of our attention to. When we practice on something with less rebound, it forces our technique to maximize any rebound we can get. And in case you don’t know rebound is crucial for how we get drumsticks in place for the next stroke (as opposed to picking them back up after a stroke.)
Splash cymbals don’t have the tension of a drum head, and with a smaller surface area and lighter mass they will be less susceptible to air resistance and inertia, which both help drumsticks bounce off of big heavy ride cymbals.
This is similar to how if you are able to develop double stroke rolls off of a pillow, then you’re going to be able to nail them around the drum set.
In answer to your question, my guess is that he is not just using a splash cymbal to replace the patterns he would otherwise be playing on ride and other cymbals, but that as you suggest he might be spending time simply practicing rudiments and anything else that you might typically practice on a snare drum or practice pad.
Is there a link to the video of him mentioning the splash cymbal? It's a weird idea, but I'd like to hear more about it to know what he's talking about.
I imagine that he means practicing ride technique, so you are not always playing through the cymbal or relying on the weight of the cymbal for rebound.