Typical political polls have a margin of error of between 3-5%. You'd expect to see to see a 3% miss roughly 5% of the time.
What's perplexing to me is that the 3% error occurred in a polling average of dozens, perhaps hundreds of polls. If it were just one poll, a 3% miss is quite within the realm of possibility. But in this case it was a range of polls that centered on Clinton +4% and itself had a roughly Gaussian distribution between Trump +2% and Clinton +10%. This makes me wonder if the polling samples were themselves not independent, or some other form of systematic bias amongst mainstream pollsters.
Obviously, it's a bit of a black eye for the pollsters. But it does not reveal that a huge number of voters hid their preferences, which is what the original comment was about; if anything, it indicates the opposite.
But was it fairly small in statistical significance? A polling error of 3% is likely big enough to confirm a consistent and very significant bias.
It's like throwing a coin and getting 52000 heads and 48000 tails. "Only" a 4% error, but sure as hell evidence your coin is biased.