No, they can't spot lies, they can only spot things they are not expecting. Tell them a short boring story if the truth is unusual.
People are always reporting odd conversations with border agents. When those conversations result in further scrutiny or being denied admittance, they can appear sinister or arbitrary in retrospect. But it's a basic behavioral profiling technique: Take a random walk down a conversation tree and look for the inconsistencies and delays that occur when the subject has to start making things up.
(You think that you're out to have fun on this exciting new adventure in life... your vacation!, your new business trip!, whatever. But they're looking for anything strange. They are bored, boring, unimaginative government bureaucrats. Give them the simple, bored, boring, short (but honest) summary of "the purpose of your visit". TFA said that getting searched is "just like in the movies!"... don't do that. Just... don't. Do not share any enthusiasm about anything with CBP.)
Something along the lines of:
"Where have you been today?"
"Santarpios."
"Never heard of it. What's that?"
"Really? It's right next to the turn off to get to the airport."
"Never heard of it."
"It's a pizza place."
"What sort of pizza did you have?"
etc. A whole bunch of quite specific questions at a rapid pace about a famous restaurant right next to the airport that carried on until his colleague had finished rummaging through my laptop bag.
http://www.foxnews.com/us/2011/08/02/passengers-face-behavio...
Your description sounds like a guy who wasn't particularly good at it. They're supposed to be direct, but not argumentative ("Never heard of it.") If they're too pushy or intimidating, it's hard to spot genuinely suspicious answers or behavior.
One of the main problems with this kind of screening is that it requires training, practice and skill. Ex-cops are pretty good at it, from what I understand, but that kind of experience is in short supply.
How did you like Santarpios?
Santarpios is great and highly recommended. Galleria Umberto's is possibly better though (and far easier to get to).
I've just remembered that when I was waiting at a gate (before boarding had commenced) at LAX about 3 weeks ago, there were about half a dozen very young looking TSA agents receiving some training at the gate about how to approach people, being reminded to keep it friendly, etc. They then wandered off to another gate and I thought nothing more of it.