That is only an accepted translation. If it was shown to you, you must have input something that the system thought was similar to it. The recommended answer is They buy clothes.
PS: I'd like to add that the best way of saying they are shopping for clothes in Swedish is de shoppar kläder.
'shop' had been added by mistake here, I've removed it again.
In English, you can say both they are shopping clothes and they are shopping for clothes, but those two sentences don't mean exactly the same thing and neither of them means exactly the same as the Swedish sentence here.