Odd gas mileage data

My Prius had about 10, 200 miles on it when I left Friday for a trip from our home near San Diego to Palo Alto this past weekend. The town I live in is very hilly, so I've been averaging around 43 mpg and was interested to see if it would be higher on the trip. (I rented a Prius in Utah last month, but stayed in the valleys, mostly on long trips, and averaged 49.5 with no real attempts to keep mpg high.) On this trip, on the way up to PA, we were getting around 46 mpg according to the display, but when we filled up, it took exactly 7.0 gallons when the pump shut off. We'd gone 397 miles since the last fillup, so something was obviously off. I don't know if my husband messed anything up, but he was so surprised that he kept trying to put more gas in it, with the pump repeatedly shutting off. On the way home, the display showed us getting about 47 MPG, and then we stopped to get gas at 330 miles, just to avoid getting gas in LA. I"m not sure how many squares it showed left, at least three. That time he put 10.2 gallons in. That's a bit scary! What could have been going on there? And now, we've gone another 150 miles, averaging 47 mpg and still have all the squares.

 

I realize it's a bit confusing the way I wrote the mileage. It's 10,200. And the distance from our house to Stanford is about 525 miles.