Some of the confusion is that virtual ground can refer either to the minus input point in an inverting op amp, or to the pseudo-ground created to provide dual voltages for an op amp from a single supply.
The op is obviously referring to the second use but his circuit makes no sense, with the resistors connected to plus and minus supply voltages and the op amp output grounded. The normal connection, of course, is the input resistors connected between the single supply and ground, with the op amp output being the virtual ground.