I don't think that's it. The issue is how to tell the screen to do a fast partial refresh at the expense of not refreshing anything else, which is what you want for handwriting. The app would need a way to tell the system what to partially refresh, i.e. some sort of nonstandard Android API.

The Boox tablets are touted for their ability to run third-party Android apps, so I highly doubt they would deliberately cripple them.