Out of 128 players in the field, they have only not faced each other in six first round ties this season. According to DartsELO the percentage of likelihood of Petersen and Webster meeting each other in exactly four out of ten events is only 0.0000746%, which means it should only occur every 1 in 1.34 million times.
This makes it even stranger and is a statistic to keep an eye on as the Players Championship Series continues.
https://twitter.com/PVDarts180/status/1114846098202476549?s=20