Yeah, it seems plausible that he thought he had to pay $29 in BTC, and so googled and paid that - but it came out 0.000004 BTC lower. And later when he found that what he paid was now $31, he also thought "well that's more than what I had to pay".
Naw, BitPay tells you the exact amount to pay in BTC for a 15 minute window. Around 10 of my friends verified I paid the right price, I was projecting to the big screen to show how it works. For some reason the network fee to pay the miners screwed up in BitPay or the price they received wasn't the right price since bitcoin went down slightly within 2.5 hours. So at the end of the day, the consumer is to blame.