That's what I meant with my reference to sampling bias.

I'm not calling attention to a sampling bias problem, I'm calling attention to a data reporting problem.

Including people who don't actively use lisp in the sample is entirely valid, and capturing that information about them would facilitate some interesting analyses. For example, we could look for demographic differences among professional lispers, hobbyist lispers, and curious onlookers. Or see if there are any industry trends.

It's just that this Google doc reports these data in a way that's too coarse-grained to support that kind of analysis, regardless of any bias concerns.