What do the percentages mean in the audio quality stats section?

These are percentiles. Call values for each of the metrics (Jitter, Packet loss, etc.) vary with each voice data packet transmitted; these are represented as percentiles. A 30% value of Jitter 45ms means out of all Jitter values that occurred during the course of a call (with each voice data packet), 30% of the values are less than or equal to 45ms. That means 30% of your call had Jitter less than or equal to 45ms.