Mum did something weird is this even legit?

Ok so she brought jumper from Primark and took off tag n label. She then changed her mind, took it back but placed the tagless one on the shelf. She then picks up a tagged one, same item n gets refunded. She did have receipt obviously. Reason is shops can be long and don't refund after tag's removed.
I was sure she get caught out but nothing happened. Got a full refund.