when it says backed by physical gold. the investors wouldn't dive for that fact all because of a claim. especially when the storage is unknown and whoever holds the physical gold. people could be trading all year around not knowing the gold disappeared from the vault....
would be great if you first read about Digital Gold project and GOLD token, everything is explained in opening post
physical gold from GOLD token is stored in one of most known bullion vaults:
https://www.bullionstar.com/myaccount/auditand is audited in real time
https://gold.storage/en/audits