The only thing that comes to my non-electrically-trained mind is that your mechanic moved one of the wires that used to go to the toggle switch directly to the ignition switch, restoring the original 'path' that provided power to the starter motor. So, originally, we have a plus wire from the fuses to the ignition switch, then from the ignition switch straight to the starter. Your lambo dealer may have 'inserted' the extra toggle switch into that outgoing (from the ignition switch) power wire to the starter, thus requiring the toggle switch to be in the 'on' position for the starter to be able to work. Your mechanic may have seen all this and decided to restore the original circuit, by routing a new wire directly from the ignition switch to the starter, bypassing the toggle switch. With no further function, he disconnected the now useless wire that ran from the toggle switch to the starter.
That, or the toggle switch was inserted in the power feed to the ignition coil or the distributor, in which case something similar: your mechanic ran a new wire from wherever the toggle switch got its feed, directly to the ignition, bypassing the toggle switch that now no longer has a function, hence the disconnected wire.