I said nothing of the sort--when I tried it on another vehicle (they were only on 510 at the time), in November 2014, it charged me two fares, per TTC fare/transfer policy, not a free transfer.
It should generally be two different vehicles--there is really no legitimate case on the TTC today where you would be entitled to a free transfer on the same car you get off of. The current discussion, I believe, is things like short turns, in which case it would necessarily be a different car.
It is important, though, that when tapping on the same car, if you happen on it by chance making your return trip, that you are allowed to pay your fare again with Presto--recent observations indicate that is not the case, but of course we have not hit the deployment date for the full streetcar network Presto implementation.
Again, to some extent this is all a bit of a moot point--we simply don't know exactly what they're doing with the upcoming changes, and frankly it looks like neither the TTC nor Metrolinx/Presto even know everything themselves. All of this is theoretical at this point, and we'll find out for sure in a couple of weeks.