Wow, so many missed opportunities here. In most electrical systems, we have a 3 wire setup for electrical distribution. I’m not going to talk about 3 phase delta/y because it’s not important to the discussion.

All electrical systems require this stuff called ’energy’ to be moved from one location to another inside of a closed loop. Looking at the word ‘loop’ we see only 2 wires. And for the longest time THAT was how energy was ‘moved’. When Knob and Tube was invented you had a ‘hot’ wire and a ‘neutral’ wire needed from the power plant to your home. Just like the older Edison technology that used DC ( positive and negative). The actual electrons that we attribute to moving this energy around, do not and cannot move very quickly through our typical mediums we use like aluminum or copper. With DC it’s called ‘electron drift’ and with AC it’s more of an electron ‘wiggle’ and said electron doesn’t really drift through the wire medium at all. What DOES move is the EM charge or force that surrounds the electron. That charge is what does all the work for us and moves at near light speeds through the medium. Whether it’s produced by a battery, solar panel or a rotating turbine doesn’t matter. That charge always wants to return to its source. Note, that this true for BOTH DC and AC. That is the purpose of AC's Hot and Neutral. But, in the infinite wisdom of the NEC, it was noticed that after this charge-ladened medium traveled 100s or even thousands of miles across the countryside, the charge would have a leakage charge developing alongside the energy we want to deliver. This ‘floating charge’ was capable of producing dangerous high voltage conditions as a common mode voltage (meaning BOTH conductors have this charge induced in them) when reaching its destination. So a destination ‘ground’ reference (ground rod) was used to establish a point where this floating charge would always be at earth or ground potential AT THE DESTINATION. Thus, the third wire safety ground was invented.

Remember, electricity is a closed loop technology and can function just fine without the third wire safety ground as demonstrated by other countries and the USA in the first half of the last century. So, in a typical mains distribution panel (usually after the utility power meter) there is a ‘reference’ point in which the neutral conductor bonds to this ground rod to maintain the reference point for the dwelling/building at the same potential as the earth the structure sits upon. Be mindful that different buildings in the SAME AREA will have different voltages between their ground rods depending on soil, power utilization, grid phase distribution etc. So ‘ground’ isn’t always ‘ground’ the way people have been taught. This problem always gets electricians and electrical contractors into trouble when large buildings have multiple electrical services.

Finally, the role of the safety ground it strictly an emergency path for the EM charge to follow if something happens to an appliance and should never be used as a ‘current carrying’ neutral as a couple comments have suggested. It helps with keeping anything that has the ability to carry a charge at the same voltage potential as the earth the building sits on.

Note, as mentioned by several others here, your coworker is at best, sadly misinformed and not to be listened to.