i just tried this and if you click the bookmarks without
command-tab, and then command click the bookmark, it still
opens in a new tab. If it worked the other way as the submitter
said, it seems that apple would have had to code it to do that,
and work against themselves. The command clicking a link is
already the default behavior, why would it change in the
bookmarks menu.

It's important to distinguish between the actual "bookmark
menu" that is found in the menu bar, and the page where you
organize your bookmarks which you get to by clicking on the
little book icon in an open Safari window. The post is referring
to command-clicking the actual bookmark menu.

For me it works as described in the original post.