First of all j-10b is in testing phase so uncle Richard can only predict things like we do here. Until the plane come in really production and prove it that's it's really capable of what it says. So before that we cannot even talk about j-10b.
J-10B is in testing phase yes - so we don't really know its capabilities.
However, you can make reasonable estimates of it's capabilities based upon the aircraft that it's based on i.e. J-10A (A solid 4th Gen aircraft which has been fully tested against Su-27 and MKK).
J-10B is going to be more advanced than J-10A otherwise there would be no point wasting millions developing it.
So is it too hard to imagine that J-10B is a 4.5 Gen fighter given that it is more advanced than the 4th Gen J-10A that it's based upon?