After a shopping trip this morning, I have a question. Is it ever ok to knowingly pick up someone else's shopping and investigate it?

I was in a supermarket earlier today, and had placed my items on the conveyor belt and talking to DS who pointed out the lady in front had something of ours. I just said 'excuse me', and before I could say anything else (I was just going to say that I think you have mistakenly grabbed my shopping), she said 'no need to be rude, I was just seeing what it was, and don't worry it's sealed'.. Um seriously, you were just checking out what I am buying?