Python code error : Hash greater than Target
It's not an error, it is a genuine result from a piece of educational or artistic software. It isn't intended to be a useful piece of software for actual mining.
According to https://github.com/muimota/miniminer
The objetive of this projects is to write the simplest miner ever to be embeded in different art projects.
So this is art, not really a serious project for any other purpose. Although I guess it does provide an educational example of how to interact with a mining pool.
As Pieter Wuille noted in a comment, It chooses just one random nonce and calculates a hash and tests to see if it succeeded in finding a hash lower than the target set by the mining pool.
Normally, for real mining, you'd maybe need to run the inner part of this (excluding pool communication) trillions of times every second so that trillions of different nonce values are tested every second. Obviously you can't achieve that rate using python, especially when using only standard PC hardware.
(community wiki, since this answer doesn't add much to the existing comments)