Owning is not the same thing as licensing. You can license things you don't own if you have a license to. The BSD license grants you license to distributed the covered code under other licenses.
Your understanding is wrong I'm afraid. You cannot license software you have not written or over which you have no ownership. It is unfortunate that some people believe that the BSD license in itself gives people the rights to relicense the work under GPL. It does not.
This misunderstanding arose from a deliberate attempt by the FSF to co-opt the open software movement by trying to relicense BSD work under GPL without seeking the author's permission. The attempt was successfully challenged by Theo de Raadt in 2007 (http://undeadly.org/cgi?action=article&sid=20070913014315) and the ensuing discussion in which Stallman was thoroughly educated in the law of copyright can be found here.
Of course you can license code you don't own. Otherwise there would be no way to have a license that allowed its recipients to redistribute and then allowed the people who received the code from them to redistribute it themselves.
I'm afraid you don't really understand licenses. A license like BSD gives you the rights to distribute the software subject to certain provisions. It does not give you the right to change the license. I can't really spend any more time on this but I'm sure people around you can point you in the right direction.
