A quick view of the system he uses comparators and function generators to create signals for the x/y/ball/paddles, which in case of the ball hitting the x/y axis limit are equal to the lowest or highest of the x/y axis triangular signal which will signal a 'hit'. But this was looked at in a glance and it is quite a lot more complex and mostly goes beyond mis simple analogue electronic knowledge.

See the link on the form post for the schematics and some example readouts of the signals.