An inference to the only valid admission: "We don't know"

After blogging about 4thought.tv's series last week, "Is it possible to believe in God and Darwin?" and discussing it during the recording of Skepticule Extra 007 yesterday, I checked out Alastair Noble's introduction video again, at the Centre for Intelligent Design's website. The video is embeddable, so I include it below:



Noble is saying much the same as he did in his 4thought.tv contribution, but expanded a little. He appears to be claiming that methodological naturalism is an unwarranted philosophical constraint on the progress of science, and that intelligent design is an inference to the best explanation. But I still don't see how "Someone did this, we don't know who (and even if we think we do know, we're not saying)" is any kind of explanation. If you can't tell how something happened, how is it scientific to conclude that someone must have done it? The correct conclusion is to admit that you don't know how it happened, and then to attempt to find out. If you convince yourself that someone must have done it, where do you go from there?