They just interested to see how westerners live, eat and do. I am sure they don't have bad intentions. What about us? Going to restaurants and see what Chinese eat..... it is to see if their food looks good.
Its not creepy.. its interest

they wanna know whay you eat and drink.. creepy

My friend came with her bf from LA, every time I took them to restaurant she would look around people's table and ask me to order food on their table.
So……
I don't see there is a problem.

I'm pretty sure the only reason I've looked at other people's tables in a chinese restaurant was to order a similar dish before I had enough language ability to order for myself.. not to look at what people are eating or buying because I am nosy.

Unfortunately...to many Chinese people Foreigners are like a constant zoo exhibit. Must watch what the silly monkey does.. "Ooh Momma! Look at what it eats! Look at what brands it buys! The elusive foreigner.. it comes to restaurants to eat too!! It buys milk just like we do! Look at it's shoes! It wears socks too! Look dad.. the foreigner buys meat! Haha! It eats food too! why does it show me her middle finger? It must understand Chinese!"

(The above comments are actual overheard conversations at my local Carrefour)

chinese do this only for curious, not only observe foreigener's shopping cart but also stare chinese's. once a old lady stare my shopping basket again and again, and finally asked"hei ,boy where you get slipper,i want buy it for my son"

This never ceases to amuse me.  I thought this was just something they do with Laowais.
You know when a couple of cute girls walk past in the supermarket and smile then look in your cart.....then start to smirk...."look at this crazy Laowai....he buy beer (lots), water, coffee, cheese and nuts.....why no chicken feet, pork or veggies?"

They are a little nosey but I think more curious, like one day I came out of the bank stood to read the document I had obtained and 2 woman stood behind me peering over my shoulder tryin to see what i was reading, I smiled and handed them the document and they ran away saying no no no

I have had the locals actually pick up the items that were in my shopping cart and go through them one-by-one.  I did not find it amusing and simply took the items out of their hands and put them back in the cart.  It has happened several times.

They want to see if you got a good deal. Maybe they could have missed a sale or something. Never seen it happen before it must be the place that you go shopping because that sort of stuff doesn't happen everywhere.

It happens everywhere...to expats.

For Mattaya, I was in R-T Mart and I don't think that is a low-end supermarket.  And yes, I agree with Derek ... it has happened to me more than once, actually several times... I find it incredibly rude..