...is that an oversight that someone neglected to remove, or does it still hold true?
It's an oversight. The licence says you can do what you like provided you retain the copyright in the files. Whether the team will offer you support in that case is another matter, of course.
I certainly wouldn't want a SimplePortal copyright there all alone.
It'll be interesting in the days to come seeing what happens to mod licenses now that SMF is BSD.
It'll be the same clusterdisgracefully insult it's always been because the vast majority of modders do not care what licence is used, are not interested and just want to share.
Those who care about it invariably err towards GPL with their heart in the right place but not understanding that GPL is, in my view, a dangerous licence with tentacles that would put certain Japanese artists to shame, not to mention totally unsuitable for scripted source files. The remaining few who took the time to understand the implications of the licences - and there are a few but it's in single digits - either go for BSD because it's what SMF uses now, or Creative Commons which actually better protects mod authors, IMO.
Incidentally, the whole copyright on a mod thing is ridiculous. Most mods end up doing vague hacks to the theme template, which causes problems, and those that don't do so via buffer manipulation. What amazes me about this is how buffer manipulation can be used for all sorts of fantastic and wonderful things and yet almost exclusively gets stuck at bodging in a line of copyright. I love what I've been able to abuse the buffer by doing (standalone mode removing the search form, the departments on board index), and I kind of hope that mod authors realise the power of using the buffer to do all kinds of awesome things, but sadly I somehow doubt it.