If you look at these details ... I would say it's more likely a C than a B:
I think the MAWS doesn't tell us anything because the tail sting was modified to have a step in it, which meant the MAWS had to be removed.
The only point of contention is the vertical stabiliser's antenna. I think that antenna is an upgrade that can be retrofitted to old J-10s, like with these J-10A/S, some of which have the extra antenna while others don't.
My conclusion is this: we've seen J-10A and J-10S with the extra antenna, so it's likely J-10Bs can be retrofitted with one too. However, we have not seen anything other than J-10Cs with the second spinal antenna. Since the TVC testbed doesn't have the second spinal antenna, it's likely not a J-10C, which means it can only be a J-10B.
Also, it has the front nose pitot tubes like the J-10B 103X prototypes, which leads me to think CAC modified one of them to act as the TVC testbed.