You can check the model of the miner by checking the sticker on the case under the control board.
Check this sample below
If the model is different from the system overview which means that the control board is replaced with s9i board or like you said maybe the owner was accidentally flashed the miner with s9i firmware.
If you still haven't tried to flash it yet with s9j firmware you can try to flash it, but make sure to backup the firmware first. You can find the backup option on the upgrade tab from the dashboard (you can use the backup to reflash it back if ever the miner experience some bad logs or it's not hashing properly with s9j firmware) then after that flash it with s9j firmware.
You can try this firmware
Antminer-S9j-all-201811071118-autofreq-user-Update2UBI-NF.tar.gz