Let's focus on getting the recovery work first. I'm not too sure but it seem your bootloader is lock or your cell was not root properly.
Is it possible to re-root again but install TWRP recovery img instead?
Once in TWRP recovery, u can then sideload other roms, that will be step 2.
His phone comes with a twrp recovery with full root.
Binary is install thru SU app.
Bootloader Is fully unlock.
Bro Is able to do a OTA update as well with no problem.
If bootloader is lock. There Is no way to Install alternate recovery and not possible to flash CM as well.
The phone can't detect OS and thus boot into recovery. It's the usual procedure when OS is not present.
It seems he is following the procedure to install back the OS but from what I read. He is missing a step.
Flashing Oppo colorOS is tricky because of partition issue. It's not str4ward and not a solution as well.
All will be fine tomorrow. Will rectify for him. Have ask the Bro to have a good night sleep.
Will post the result tomorrow.