I agree. Actually even if hypothetically Dalvik was proprietary software, this would still be an attack against Free Software - prohibiting new implementations goes against the very core of what Free Software stands for.
We now know for sure that all independent Java implementations (and there are quite a few of them, including GCJ) are at least as vulnerable as Dalvik. If Oracle wanted, they have the means to shut them down. They won't bother simply because none of the alternative implementations has become important. That is not very reassuring.
So how is this not an attack on free software? I would say it is the single biggest attacks since SCO. In a sense it is even bigger because while SCO was on shaky ground from the beginning, Oracle is _extremely_ likely to win this case in court.