Lecomte was a relative of Jomini's, I believe, and his account probably needs to be taken with a large salt pill.
Jomini's initial employment was as a civilian, though he insisted on wearing his Swiss uniform when 'on duty.' I doubt that the colonel was jealous of Jomini, but merely annoyed as Jomini was making a major annoyance of himself. I cannot see a French staff officer of that rank being jealous of a Swiss civilian. Jomini was overcome with the thought of his own importance and he believed he knew more than anyone else.