What they saw

This is a simplified diagram of how the sculpture looks like. What the audience really is seeing, is a 'squashed' cylinder, with a cross-section of an ellipse rather than a perfect circle. Nothing wrong with the camera, the sculpture is made this way.

Instead of a circle like this
It is an elipse like this

How it is done
How this trick is managed is actually rather simple. What the sculptor did, to produce the optical illusion of a perfect cylinder (from two viewing angles, that is), was to sculpt it in such a way that it is "compressed" not from a perpendicular angle, but at an angle like in the diagram below, so as to create the illusion of how the circular cross-section would look like when viewed from an angle.

Not compressed perpendicularly
But compressed at an angle as shown