Rule 163 is not a model of clarity, but I don't think Rule 163 requires an athlete to be disqualified for jostling or obstruction.
Rule 163(2)(b) says that an athlete who is responsible for jostling or obstruction "shall be liable to disqualification." I read "shall be liable to disqualification" as meaning "may be disqualified." In other words, disqualification is discretionary with the Referee.
You can compare the language of 163(2)(b) with the language of 163(3) on lane infringement that was used to disqualify Kemboi. For lane infringement, "if the Referee is satisfied ... that an athlete has infringed this Rule, he shall be disqualified." For jostling, the athlete "shall be liable to disqualification," while for lane infringement, the athlete "shall be disqualified." Presumably, there's a distinction intended where the Referee has discretion not to disqualify an athlete for jostling but must disqualify an athlete for lane infringement (subject to the exceptions for being pushed or stepping out on the straight).
The bottom line is that Mead could be reinstated without the Referee being required to disqualify Farah. Being a stickler for the rules does not require Farah to be disqualified.