I think the fact that the wait staff at the tapas restaurant observed the McCanns acting "normally" is just another piece of information to add to the picture. I don't think you have to be an expert in human behavior to evaluate whether someone is acting normally. We all know what "normal" looks like, in the same way we all know *advertiser censored* when we see it, even if we can't define it. It means they weren't behaving suspiciously, nervously, or emotionally, etc. And, the wait staff had been watching them come to the restaurant for five nights already, so they even had a base line for comparison. So, the McCanns were acting the same way they had acted the other five nights, which was the same way most people act when their eating out with friends.
We got a couple of other pieces of information. It wasn't an all out booze fest, as some papers have claimed. It was five or six bottles of wine, which among 9 people over several hours isn't all that much.
Also, we learned that the McCanns couldn't actually see their apartment from the table (although that wasn't surprising, as it seemed pretty obvious from pictures to me). And, I appreciated his take on the McCanns that night. I can see his point that they had probably been lulled into a false sense of security by the previous five nights of leaving the children and eating out. If everything had gone well for five nights, they may have gotten pretty lax about their checking routine. Between that and the wine and good conversation, they may have only thought they were checking their children every thirty minutes, when in fact more like 45 minutes to an hour was going by between checks.
And, I appreciated his observation that the McCann's regular routine and the location of their apartment were both conducive to an abduction.
None of this is compelling proof that she was abducted. It's just more information to file away.
Despite all this, I thought the show was pretty thin on new information and not "explosive" as their promos claimed.