Hey there! Great question - I'm not 100% on where on the fretboard Skynyrd played it, but the beauty of the guitar is that sometimes you can find other positions to play the exact same notes. So, playing those D octaves in open position is absolutely fine in this situation.
There are other situations where it might not make sense to do that (eg. if the part called to slide up or down from those octaves), but in this case, go for it!!
Mike
Keep rockin!
Mike Olekshy
GT Guitar Coach