To quickly answer your question: You’re free to use whatever numbering scheme you want as long as it gives the correct output.
As the output shows, there is absolutely no difference between a list numbered with any 0 or 1
0.
0.
0.
and a list using the actual numbers that appear in the output as well:
1.
2.
3.
The first number you use is the starting number for the list (but both 0 and 1 give 1), so to begin with 4 you could do 4., 5., 6. or 4., 4., 4. or even 4., 0., 10., the output is the same. I guess in the case of your answer the editor just wasn’t fully aware your syntax was fine.
The formatting help says:
A numbered list:
1. Numbered lists are easy 2. Markdown keeps track of the numbers for you 7. So this will be item 3.
I’d say this means essentially what I wrote above: Output matters, the rest is up to you.