A QR code is essentially encoded text. It can be a URL, a poem, what you want for your birthday, your local library library hours and so on.
Now, if you choose to go to a linked website that you find in a QR code, then that website knows typical analytics like location, browser, and device type.
This is one of the things I dislike about the iOS platform: it is completely unclear what kind of data these apps store about you somewhere.
In all honesty I did not think of that scenario!
There could be some data harvesting on the back end from an app, but there are quite a few barcode/QR reader apps out there that one can easily choose another app.
This type of data harvesting can happen on any operating system. Just because it isn't reported, doesn't mean it's not happening. :-)
On the mac there is a utility called Little Snitch that allows you to allow/disallow connections that applications make to the internet (even hidden ones) if you don't want your data to be out there. Nothing like that on iOS though (that I know of).
I suspect that any connected device can collect and transmit information. I read recently that some apps on smartphones have hidden capabilties to do such things. One has to be quite diligent to examine them all! Thanks for the tip on the Little Snitch app. I'll look into that.
In reading the given articles in this course, it seems to me that data collection has been a long time initiative (and at times with little intention to analyze). It is quite amazing the types of information stored. Now, to figure what to do with them.