I have a memory of a previous similar incident, perhaps that was yours?
eLearn diagrams for the x250 show a CAL4 fuse, rather than the CAL5 that you mention. This raises the question as to it being previously replaced.
Perhaps worth keeping in mind that the CAL fuse also protects the alternator and associated wiring.
If the starter is jammed, or there is an earth fault then it is possible that the CAL5 fuse was blown by jump start attempts, but why did the engine stop while driving. If you postulate an intermittent fault in wiring protected by F03 (ignition switch) then that is possible.
Why did F03 blow when you attempted to start the engine? I have a niggling thought that the eLearn diagrams may be over simplified in that they only show one winding on the starter solenoid. Certainly starter solenoids used to have two windings. A high current operating winding, and a lower current holding winding. The high current winding was earthed via the starter motor and shorted out when the solenoid contacts closed. For an illustration see attached x230 diagram. If solenoid does not close the main contacts, then it may be that F03 cannot carry the maintained higher current? I do not know for certain.
I am still struggling to link the failure while driving on several occasions, with F03 blowing when subsequently attempting to start. I keep thinking wiring fault. If for instance the main starter cable (including alternator and connecting cable) shorted to earth briefly, then this could perhaps drop the voltage sufficiently to upset the engine control unit?
I am sorry but I do not seem to be able to do other than offer suggestions.