Wikimedia Bugzilla is closed!

Already got couple feedbacks saying they thought it counts # of chars instead of
bytes.

I'd say # of chars would be more intuitive and more representative.

On the other hand, if not possible, just add the word "byte" / "bytes" behind
the number to make obvious what is being counted.

Should also be able for l10n, I'd suggest something like [[MediaWiki:Bytecount]]
(because it can be reused later somewhere else) with default like
{{plural:$1|byte|bytes}}