May I ask of your observations? Were you on the flight or just an on looker just interested that's all...
Anyway, to have the airbridge off at 7:50 after chocking at 07:17 is pretty good going IMO. Potentially the tug bar / tug could have been connected during boarding or before airbridge disconected to help speed up push back time should it be available, however this depends on type of tug, availability etc.
Air Berlin schedules a 45 minute turnaround at most airports, Stansted included. To what your ''timings'' are showing, Servisair achieved this if not much quicker! The only thing that could have delayed the push back departure will most likely have been ATC for ground clearence etc, so what do you mean ''is this normal service for air berlin''??