I could be wrong, but I don't think the M3 was even in the mix. Do they even have enough data on reliability to rate it? If not, that will disqualify it right away. Plus they made a point of saying it was the best value for the price of 35k. Who knows how much that weighed on the pick.
Anyway, I don't think they picked this over an M3 for best sports sedan. I have never driven one, but sat in one at the car show last year. You better close your eyes because the interior is classic cheap GM interior and don't touch anything either.
Maybe it does drive great and is a good value in the segment. I still find it hard to believe that it is better than ATS, 3 series or A4s etc.
I'll never know because I have zero interest in the car.
Edit: I also don't think R&T has anything to do with it. They are just reporting CRs picks for top cars in the segment. Thread title is a bit misleading.