Why is the pattern displayed in the Polar Meter different from the selected pattern?

All microphones have patterns that don't exactly match the manufacturer's stated response. In other words, there are no "cardioid" microphones with perfectly cardioid polar patterns, just as there are no omni or figure-8 microphones with perfect patterns. It's not possible to design and manufacture capsules with perfect patterns.

Also, polar patterns are always somewhat frequency dependent, which means the pattern is different at different frequencies. As a consequence, there is no single pattern that perfectly represents the microphone's response. And because of proximity effect, the pattern at low frequencies is also distance dependent.

The Sphere plug-in display the best approximation to the actual pattern at about 1kHz of the specific microphone we modeled, even if this is different from what the manufacturer states as the pattern. It should also be noted that in Off-Axis Correction mode the Sphere microphone can achieve polar patterns that are much more accurate across frequency than most microphones.
The Sphere Technology Whitepaper might shed a little more light on this.