I'd argue that TAR28 had at least 3 teams with similarly sized (if not bigger), similarly dedicated fanbases as Jody who were also similarly uninterested in TAR before their team was cast. Yet there was a negligible impact on viewership.
The existing fanbases of these pseudo-celebrity teams together can certainly account for some new or returning viewers. But as has been pointed out, the Wednesday timeslot and premiering in this holiday-like week are much bigger factors for such a sizeable jump.
As huge as these premiere numbers are (and whatever the next week of DVR viewing might bring), I'll echo Peach saying that it will be interesting to see how next week goes. And the following weeks. This big premiere definitely gives TAR a much bigger cushion, especially as it heads toward the double episodes and then against the Olympics.