Eh. Chargen is definitely something, and it's engaging with the rules. It's lacking the interactive and social aspects, but so (arguably) is something like Thousand-Year-Old Vampire. (Yes, the latter is specifically written for solo play, there's still no social interaction happening.) Session prep seems to be something similar, though given that it's intended and expected to land on a table where people are playing the TRPG, it's probably harder to argue for it as "play," though there are certainly people who derive a good deal of pleasure from it.