Yes: why would Dumbledore allow McGonagall to think that Voldemort only had one Horcrux?
“Perhaps not, then,” Dumbledore said after Minerva tried to explain. “I confess I had been hoping for something that would help in finding Voldemort’s horcrux, wherever he may have hidden it. But...” The old wizard shrugged.
Yes: why would Dumbledore allow McGonagall to think that Voldemort only had one Horcrux?
This is a very good point.