I and some of the others are interested in seeing how this happened, and possibly getting it fixed in the client or server software so this misconfiguration will be caught in the future. JimboPalmer's advice has its merits, and you have followed that approach now that the WU has completed.
As I mentioned, there have been a few reports by OS X folders in connection with GPU folding. The ones I recall were on the official reddit, and information on how they got a slot configured that way was not provided. Also not available was the configuration information from the client log. With your report on a Windows system, this shows that there is a bug in the common code of the client or possibly at the server level.
You did mention that you set the GPU Index value to 0, that might be important in tracking this down. Normally you don't have to change it from the default value except in some cases involving multiple GPU's. In any case the slot is identified in the configuration info as a GPU slot.
Looking at the first log in your post just before this, I see that the first WU processed on this "GPU" slot was from an A4 project. That download would be shown in the log older than this as it and the WU for the other slot are already on the system at the start of this log. It failed with an IO_Error. I can't tell if that is related to the configuration of the "GPU" slot running a CPU folding core or something else, but the WU did go on to be processed successfully by someone else.
Then the slot downloaded the A7 WU and the processing core to use for it. For whatever reason the slot was treated as a CPU:1 for the request, so once assigned at that setting it would not use any more CPU threads.
Finally, one question that you raised was about the availability of A7 WU's. Currently they appear to be in low supply, I don't know of a specific reason for that. I could guess that older A4 projects might be getting a higher priority so the research on older projects could be finished, or that the persons working on the newer projects have the results they need for now and could be back later with more work. But those are just a couple of the possible reasons, and might not apply.