By default, package setspace interprets it the same.
But no rule without exception. So, we do not really know, how someone else would interpret “single spacing”.
However, if you want so setup a smaller leading, package leading could also be useful. However, you should note, that removing the leading completely could result in unequal line spacing of paragraphs because of superscripts of footnotes or height and depth of inline math.
Sorry, but I can no longer participate here as the administrator is trampling on my wishes on one of his other platforms.