Report on BMW includes Mini cars, so BMW can thank Peugeot/PSA/Citroen for the good ranking, it seems.
BMW gets most expensive repair per occurrence, so its like russian roulette, it's unlikely to shoot, but when it does it hurts "real bad".
On the VW front, Audi is included, and fares significantly better (why is a good question to ask VW executives, as many parts are identical, there must be some corner cutting involved in the assembly lines, maybe due to assembly in Mexico/USA compared to assembly in Germany for Audi ?).
Honda/Toyota and friends score big in term of "problem free" models. Some lines of car seem to just work forever according to the detailed report (list of most 100 reliable individual cars per model and per year). One conclusion that explain low overall rating is that while they have problem free models, the brand is plagued with lemon models that pull the overall grade low.
BMW individual models score just average, and the x28 and x35 cars are merged, which means the problematic turbos get diluted into the large mass of NA engines per year.
There may be a systematic bias due to BMW long factory maintenance, that is probably not reported (BMW dealership are ASE ? ). Problems arising in the first 4 years of the car are probably not reported while other brand see problems being reported after yr1 of ownership.