He is (technically) right, your passive bass has a high impedance output matching the impedance of the passive input.
When going through a preamp or a pedal, this signal becomes a low impedance, so has to go to the active input to have input and output impedances matching.
You should have trusted him, because of his background. It's like not trusting the surgeon saying he has to put back that finger that you stupidly cut with your very sharp new knife.
That said, you can live with one finger missing as you can live with the wrong input, it doesn't make a great difference...