Hi,
This mod works only on links included within user posts. (e.g. using the URL bbcode).
The link you mention is part of the postbit template. You can add the rel="nofollow" manually by editing the corresponding template (e.g. postbit or postbit_legacy).
For instance, in vb 3.6.8 the template snippet looks like this:
PHP Code:
<if condition="$show['homepage']">
<tr><td class="vbmenu_option"><a href="$post[homepage]"><phrase 1="$post[username]">$vbphrase[visit_xs_homepage]</phrase></a></td></tr>
</if>
Hope this helps.