On some networks, yes: I used to use a prepay mobile network (= buy a fixed quantity of GBs in advance, use them, once you run out, you get a restricted captive portal where you can buy more, just like on this flight). But all traffic on port 53 was allowed, it didn't need to be actual DNS traffic.
There's even some commercial VPN providers which offer openVPN on port 53.
If they had a ssh server on the remote machine they could have also done something like `ssh -g -ND 53 root@localhost` from the remote machine, which would have exposed a remote-accessible SOCKS proxy on port 53.
There's even some commercial VPN providers which offer openVPN on port 53.