I've not had this trunk problem my on 2018 G80, but intrigued by this issue. If you'd like to troubleshoot further please provide the following.
Q1) Does this ONLY happen at the same location (i.e. only at home in the driveway)?
Q2) When this happens does the trunk fully open or just 1 or 2 inches?
Based on information provided, it is highly unlikely it's another key fob/garage opener triggering this. You could rule this out by having the dealer reprogram/reset all of your key fobs/smart key cards.
The technology for the auto trunk is passive (Passive Key Entry and Start-PKES) and is likely the same used for the keyless start. Passive meaning you don't push a button on the key fob. The key fob unlock/lock, Trunk Opening and Alarm is an Active system (Remoteless Key Entry-RKE). This is Active because you have to push a button on the key fob.
In modern vehicles there is a unique key/secret/code for each vehicle and is typically secured using cryptology/rolling code technology. This makes radio frequency interception and replay attacks difficult/time consuming to do.
My current hypothesis are ...
1) Mechanical issue - The trunk latch is barely holding the trunk closed. As the vehicle cools overnight the latch shrinks allowing the trunk latch to release. Also consider, the trunk latch release solenoid or wiring is damaged/malfunctioning. Answers to Q1) and Q2) above will help vet this theory.
2) There is a key fob/smart key card hidden/lost in the trunk (previous did owner this maybe). Verify you have all of the key fobs/smart key card. This is unlikely as it would constantly trigger the trunk opening.
3) Some else has their fob/garage opener programmed using the same secret code as your car. This is accidental/not malicious. This is highly unlikely in modern vehicles. Contingent on number of bits used for encryption there are BILLIONS of possible secret codes.
4) A bored teenage kid has captured your key fob RF signal and cracked/decrypted the secret code. They are being malicious and f@cking with you. This is unlikely in modern vehicles using better encryption and longer keys (more bits), but with enough computing power this can be brute forced/cracked with enough time.
Each manufacturer likely uses proprietary technology and thus it may vary in implementations. I haven't found specific documentation on how Hyundai/Genesis has implemented this yet.
Some reference material follows
Smart key - Wikipedia
Are RFID ignition systems secure?
How Does A Small Device Lock/Unlock A Car From A Distance?
https://www.usenix.org/system/files/conference/usenixsecurity16/sec16_paper_garcia.pdf