Subdivide SOP is updated to use the new hscript expression vertexgrouplist that's added in Houdini 18.5, rather than having to use VEX to store the same vertex group list, which is more expensive.
I filed this RFE while I was working on Pragmatic VEX: Volume 1, so SESI added it in 18.5. The course has also been updated to mention this with the release of Houdini 18.5.
https://www.dropbox.com/s/f3s2cfx0ew2qu5f/Subdivide_SOP_Animatrix.otl?dl=1