Since this was a routine inspection of the pump impellers and intake shaft I assume the job was to be done with the pump off. You are absolutely correct in that the pump should have been locked out. However, only the main power source to the pump motor needs to be locked out. I'm assuming this was a 1200 VAC or higher voltage motor. These motors have large breakers that can be opened and racked out of a cubicle. There usually is a switch on the front door that must be pulled (opened) before the breaker can be lowered and racked out. This should be done after the breaker has been opened which is done when operations shuts down the pump. It makes no difference if the control circuits are de-energized or not, whether they are manual or automatic systems, or how simple or complicated they are. The only safe way to lock out equipment is to open a switch or breaker that feeds the motor itself. For 440 VAC breakers pulling the switch not only opens a circuit to the closing coil but also provides a mechanical interlock that prevents the breaker from physically closing even if there was a short circuit in the control system. For rack out breakers there is a physical separation between the energized side and the load side of the motor circuit that makes it impossible to provide contact to start the motor.
In the steel mill I worked in we had a pit outside that collected flume water which had scale in it. Occasionally, we would have divers go to the bottom and clear away the scale and debris that had collected around the pump intakes. This was a closed water system. To lockout a pump a trained electrical maintenance person would accompany the diver to the pump breaker. The electrician would verify the breaker was opened and then pull the switch. He would lower and rack out the breaker and would have the diver place his lock on the switch. The correct procedure was very detailed and specified in an SJP (Safe Job Procedure) of which the diver (company) had a copy of. Only the diver performing the job could put his lock and later remove it from the switch at the completion of the job.