No, the puzzle is between 2^63 and 2^64 BUT:

https://github.com/brichard19/BitCrack/issues/223

(uint64_t)_points * _threads * _blocks;


So instead of checking all keys you are basically ignoring alot of keys. If you have e.g. 512 blocks and 1024 threads (doesnt matter if those are valid inputs) you would basically jump over 512*1025 = 2^19 keys.

So thats why you are faster finished.