That's just using each character as a number.  Did you try converting it to the binary representation?  for example, 11 in base-62 equals the number 63

I unfortunately have to leave right now, but my prediction is that if you took z69JZqlJn862D1ndx7oLVEMmV0lP1zewEeUCrsI7Roahzpeny7P and converted it to the binary representation, assuming that's base62, you'd get a dogecoin private key.