Yes, by default it use cellular network time, previous discussion below:
Some changes is needed to make update via NTP over Ethernet automatically.
For the manual command, just tested and it works for me to update time over Ethernet.
root@swi-mdm9x15:~# ntpd -q -p pool.ntp.org
root@swi-mdm9x15:~# date
Sat Jan 1 00:09:42 UTC 2011
root@swi-mdm9x15:~# date
Thu Jul 5 11:55:42 UTC 2018
root@swi-mdm9x15:~#
Any chance the NTP server is not accessible or blocked by network gateway or firewall?
One bad thing about “ntpd” tool is that it does not return the execution result, tcpdump capture may help to check further.
Hope it helps.