between investment and mining has its own advantages and disadvantages, but I think if you are afraid of risk then you can use mining method to get bitcoin, because if you mine you no longer need to think about the issue of bitcoin price fluctuate, because whatever bitcoin price you will definitely get it if by way of mined.
What the notes is saying is if you mined bitcoin you will get it anyway but if you pay for it you will need to spend your fiat to buy it. The difference is one is free to buy but then you need good gpus to be able to mine it which not everybody has got.