I am in space all by my lonesome. I can't see anything. I am in a gravitational field. What fictitious force am I experiencing? You said the distortion of space time causes a fictitious force. What is it?
Gravity?
Where have you been for the past 15 pages?
Careful, you forgot to say from the reference point of either the source of the field, or a distant observer.
But given that he said experiencing the force, it would be better to answer with the tidal force caused by the field, because the person in the field doesn't feel the gravity pulling them to the source, they only feel the difference in gravity between the part of their body closer to the source and the part futher from the source, this is experienced as a slight stretching, normally too weak for a human to feel.
The engineer has also forgotten something important, while GR does say that a person in a gravitational field stay stationary(stationary meaning taking the shortest path through spacetime towards the future), the source of that field stays stationary as well.
He also keeps forgetting that the equivalence principle only applies to local experiments.