I had viewed that video and found this as well, "Trace is not completely sure of his findings as yet and needs to do some more tests. He notes that this only seems to occur when using the V-Log picture profile".
It appears that the S1 requires the V-log software key for the dual—assuming that his findings are to be verified—to be operational and thus it is not clear if the dual native ISO is available while shooting stills, while the S1H's dual native ISO is allegedly active at all times. But the dual native ISO is not the only advantageous feature of the S1H. That said, while there are many S1 owner/users out in the wild, I find it odd that no one else has made mention of the dual ISO, unless those individuals have avoided purchasing the V-log key.