Everything in root is played by the date/time, the order in which the files were placed there. If you paste 001.mp3, 003.mp3, and 007.mp3 - in that order - it will play 003.mp3 when you send a command to play '002'.
The files placed in a folder will play faithfully - by their titles as you expect.
Well all except who you mark as solving the problem.
You didn't credit the member who told you the vital information needed to solve your problem. Yes you verified that this was correct but you didn't actually solve the problem yourself did you?
Those of us who answer questions on here are doing so for free, out of community spirit. Please thank people who provide helpful answers and don't forget to give s as well.
It also helps if you click the Solution button at the bottom of the reply that answered your question. This will make it easy for helpers to see that it is solved and for others with the same question to find the answer quickly.
So that is the reply that answered your question not the reply where you verified the advice given to you.