Someone correct me if I'm wrong but I don't think there was an STI in that video. From what I can tell, these were the cars:
Subaru WRX (manual)
Subaru WRX (auto)
Subaru Legacy B4 (auto)
BMW 130i (auto)
MS3
Clearly the MS3 would have reined in the 130i and WRX if it were a longer race but I'm fairly certain it had a couple of obvious advantages. One being that it had a manual as opposed to the auto-equipped cars (notice how it passed the B4 and auto WRX so easily) and it may have been one of the only cars in the test with dedicated summer tires. Although they don't say, it's very possible that at least a couple, if not all, wore all seasons.
Not trying to diss, just thought I should point that out.