You missed the point. The rule is in the morale section
...in the 'Regrouping' subsection.
You want the fact that the rule appears in this section to obviate it from applying anywhere else.
No, I want the fact that it is never referenced anywhere else, and that the Regrouping section does not tell you to apply it anywhere else, to mean that it does not apply anywhere else.
Position A, where the tank doesn't get pushed off the table. Here you are required to edit the tank shock rules to allow a move that is not the shortest. I almost never get on board with rules readings that require me to add text because its a little to AFDI for my taste.
No editing is required. if you assume that a model can not move off the board unless Falling Back or Deep Striking, then moving it off-table is not possible, in which case moving the vehicle sideways instead of off-table IS moving it the shortest distance possible.
No creation of rules required.
On the other hand going for option B, and moving it off table as you suggest, requires the assumption that the rules for models that are Falling Back count for any model touching the baord edge, and the creation of a rule that makes off-table vehicles count as casualties.