This looks definitely lean and might be caused by pre ignition due to being overly lean. There are no DET marks on the piston crowns. Pre ignition is the worst that can happen. Temperatures and cylinder pressures can go skyhigh in the blink of an eye. Many times it cannot be heard in the DET cans and no knock shows up. Even AFR may not show excessively lean as most people measure average AFRs of all 4 cylinders.
Most likely faulty injector or perhaps a clogged one. Also check wiring to make sure injectors are ok and clean mating connectors, etc.
Good luck on the rebuild.