Would Ocon have been landed a 10 second penalty if he was himself lapping a back marker?
No, not if he was lapping a car and other car was in Max position - the other car would be under blue flag and should not interfere with overtake. The other driver would get penalty, anything from 5 or 10 secs - or possibly 10 sec stop go.
However if Ocons move was either:-
(1) trying to unlap himself from a tail ender -
he could still face same 10sec stop go penalty, but more likely a 5 or 10 sec added time penalty.
(2) racing for just for position -
other car might get 5 sec added time for causing collision, or more likely IMHO be regarded as racing incident with no further action.
Having set out these various scenarios we still all know stewards decisions can be so variable as to make it impossible to say with real certainty just what they might do.