Of course, it checks the check digit. Did you look at the source?
It's still possible to get a false positive that passes the checksum, but it's quite unlikely. Are you sure you are not seeing another format in the false positive like UPC-E? Usually this happens when the barcode is not readable and you sit there scanning for 15 seconds. Eventually there's a false positive.
The frame size is set that way on purpose. Larger frames induce you to hold the device quite close. That's good if the minimum focal distance is very small, but that is not true of most devices.
You are using an old version of the code, from a time when the average screen resolution was lower. If you use the latest you'll see that this has already changed to be larger to better match modern devices. Use 2.1 / HEAD.
Why scan for anything but EAN-13 if that's what you're looking for?