Can anyone explain the reasoning behind this post?
"Weight of $-4$" seems to be the key thing you're missing.  Translating a little, the neuron's value is $\operatorname{relu}(5-4x_1-4x_2)$.

Oh, and there seems to be a typo in the post:
"Then, if X2 also gets switched to 0" should be "switched to 1"