May be this happened: AllWinner made x64 ARM chipset and decided to put everything possible on the chip including HDMI. Too many features broke the power budget for tablet/phone, so the only solution left is to stay constantly AC power connected. One possible uses is home theater, but this requires to talk to middlemen in media streaming, and those do not need x64 bitness that bad.
So I think that it is home theater chip being marketed as PC. May be it is result of some early x64 project by Google+ARM+AllWinner to have more x64+ARM+HDMI for TV platform, and later chip was finally made, but nothing happened around TV/Home theater direction.
I think so, because TV does not need powerful graphics. If graphics was powerful the guys would have some game demoes for it.
Or even may be the chip is general purpose server farm kind.