I don't know of any way the software could generate that code for you. It's more likely that at some point someone added the first condition and forgot to delete the second one, or just left it there (since in this case the second one doesn't do anything when it's inside the first one).
In any case I think you want something like this:
Code:
<vb:if condition="in_array($vbulletin->GPC['forumid'], array(48,66,67,-1))"><table width="100%" style="background-color:#ffffff;">
and make sure 48,66,67,-1 is what you want (I don't know what -1 does). Also, you will have to remove the corresponding </vb:if> (which isn't in the code you posted).