Finding Equivalent Thevenin Resistence
I assume for node 2 you're ignoring everything to the right of it?

Anyways, to calculate the Thévenin equivalent, you look at short-circuited current and open-circuit voltage. If you just want resistance (if you have VTh and ITh, then R = V/I), replace voltage sources with shorts and current sources with opens.

For just resistance, if we replace the 10 V DC source with a short, then we can see that it's just two 10 kΩ resistors in parallel just like your guide shows.  To check it, we could find VTh and ITh. 

VTh = 5 V, a simple voltage divider between equal resistors. ITh = 1 mA (10 V, 10 kΩ).

$$R_{th} = \frac{V_{th}}{I_{th}} = \frac{5\mathrm{\ V}}{1\mathrm{\ mA}} = 5\mathrm{\ k\Omega} = 10\mathrm{\ k\Omega} \parallel 10\mathrm{\ k\Omega}$$