Your provided link does not take me to any kind of survey results.

Regardless, I think it's safe to assume the Stellar Foundation polled their own users, and not a representative sample of the general population. "Cryptocurrency enthusiasts use cryptocurrency" is not exactly an interesting or surprising survey result.

The survey results I saw, the important citations I didn’t see is how they extrapolated the results to represent anything more than the responses of 2,079 people that are interested in surveys about cryptocurrency and cross-border transactions. Therein lies the rub.

So what does this have to do with 8 million people?

If the survey was of 2,079 people, then how does this extrapolate to 8 million? They say 23% of the respondents represent 8 million people, but that does not mean that 8 million people actually used crypto.