[Edited to add: from https://en.wikipedia.org/wiki/Network_Time_Protocol: "Asymmetric routes... can cause errors of 100 ms or more."]
However they use the closest NTP time server, so assuming the NTP server owners correctly are able to sync their own servers, the offset is probably close.
Unless the asymmetric delay is on the path which both the ping and the NTP synchronization take
Assuming the NTP server is not on the LAN using a GPS (or other radio) reference, a large part of the asymmetry is on the poster's VDSL last mile hop. At least on my bonded VDSL2 line, it seems there's significant asymmetry; I found with regular ntpd I needed to delay incoming packets by around 18 ms to get a good match between a GPS receiver and network servers; my round trip time to the PPPoE concentrator is about 21 ms, and I was able to find a few NTP servers close enough that round trip to them was about 22 ms; not much room for additional asymmetry there.