Resistive Touchscreen Stands in Midway of the ADC in standby
Hi Z stands for "seemingly almost nothing connected", it acts as an open circuit, so you should take care of that situation if you want the other circuit to function properly.

Also, by the looks of it, 4.7k seems to be right in this scenario, as it would mean ~1mA at 5V, which is usually tolerable by most of the devices.

You should take a look at the uC datasheet on what resistance it uses for pulling down, and probably just set the port to pull down and the direction to input, but that might depend on what output impedance the touch module provides...

Copied form my comment below

According to the doc In stand-by mode one of the lines are connected to a level triggered interrupt in order to detect touch activity 

It seems it stands for interrupt - if the device is touched, and goes out of standby, it pulls the line low to make the uC aware that it is touched. The uC has to switch mode of that pin to ADC at that time, and then it can detect the coordinate.