INI format doesn't have a "standard", and indeed according to wikipedia it's not defined whether commends have to start in the beginning of a line.

But de-facto modern implementations (see python, iniparser, etc) allow the following:
var=1000 ; bigger is better

So yes, back in the DOS days comments had to start in the beginning of a line.
I don't think this is the expected behavior from a modern ini parsing library.