The other answer didn't get the problem with the sentence.
The sentence is intended to communicate that message that the bathrobes explode when you leave the house with them and you don't have permission to leave with them.
The problem is that it doesn't. It doesn't say that the bathrobes explode when you wear them while leaving the house. It says that they explode when you leave the house without authorization regardless of wearing them. The idea that a person leaving the hotel without authorization causes the bathrobes in the house to detonate is silly.
Alternatively you could read it as being about the bathrobes being the subject of the word "Verlassen" but that doesn't work either. You don't authoritize bathrobes to leave. You can authorize people to leave with bathrobes. Dropping "unbefugtem" makes the sentence work.
At least that's the error that the editors of the Spiegel saw in the sentence. You can argue that it's possible to still understand what's meant, but that doesn't make the sentence correct.