Yeah, partials do affect your overall mileage because we count all fuel-ups when calculating mileage. That's why this situation can happen once in a while.
We calculate average MPG by taking all miles driven divided by total gallons filled. With your car that's 751 total miles / 14.098 uk gallons. That gives us 53 MPG even though no individual fuel-up is that high.
Over time, including partial fills gives us a more accurate picture of your average than leaving them out. Once someone has a couple dozen fuel-ups this rarely comes up.