Can they find it who did it? And if so does the takeaway know? Or Just Eat or both?
JustEat will know who did it via registered user, the takeaway doesn't need to know the user just the details of the order and delivery address, basic GDPR
Can they get the IP address and trace it to the person?
Fuck no, firstly because that data is not required, and on top of that it is simple for someone to order on a phone and simply use mobile data, or if done on a pc use a commercial VPN (even though that traffic is monitored), for a small scale fake delivery then no, no one is going to investigate.
JustEat have policies in place already to block users who try this, and if the restaurant follows policy with feedback it helps the algo (which most do as they are losing money).
More often than not it will be an innocent mistake, I kept getting deliveries as the postcode is the same and our street names are interchangeable on Google/Apple maps, even doctors fucked up with some sensitive post, ended up getting a lovely christmas card from her at the start of lockdown and a nice full on curry.