It could be expectation , you go into Aldi and Lidl expecting it to be cheap crap and are pleasantly surprised when it isn't ...
As someone involved in blind testing all I can tell you is that when we blind test their products v some other stores and brands , Aldi and Lidl pretty much always come last , on the whole it tends to be the major brand that comes first , there are some exceptions , Waitrose own brand OJ tends to out perform Tropicana for example .( though if you are a regular buyer of those products , In a lot of cases you'd would be able to identify it by the familiarity of its appearance or taste ) ..
One of my regular projects is visiting every supermarket chain and purchasing some product for internal testing , as part of it I usually have a good mooch around the store , Lidl do some excellent macaroons , Asda have the strawberry cheesecake flavour Milky bars , Aldi do a great crème brulee nougat and some fairly sizeable Big Daddy steaks .... generally I'll eat any brands I'm not fussed , but the Aldi fake peanut M&M's are not as good at the real thing , their Seal bars are as good a penguins though