The process you tried was to spend loads of time on carefully designed interview questions which then get used to filter out candidates.
The OP was not suggesting this approach, but instead suggested engaging in a friendly conversation about technical interests and recent projects.
I can see why the first approach might fail, only because it isn't that difficult to memorize several answers for well know questions and topics.
However, to hold a conversation on a particular topic would require a greater depth of knowledge, so I can see how this would be much harder to fake.
I suspect the second approach is a lot like how police catch people out who are lying. As number of lies grow it just gets harder and harder for the individual to keep all the lies consistent and coherent.