Privacy in PIVX comes from zPIV. The wallet generates a zPIV deterministic seed. This is sorta like a private private key. This allows you to access your zPIV balance. zPIV is actually stored in accumulator addresses so no-one can see who owns them unless they have the zPIV seed.
on chainz in the rich page it shows a total wallet count of 63,326. is that or could that be the total number of wallets in existance. So for each block each of those wallets has a chance propotional to the amount of piv or pivz stored under that wallet number.