I appraised a house last week --county records showed 4 bedrooms, 2car garage. 2,140 sqft MLS --3 bedrooms 3 car garage. 2,140. My measurements 3bd 3 car garage house 2,000 sqft. The additional sqft was in the garage not the living area. I made detailed notes in the report about my measurements.
A two story home can be off too. The stair case, open areas, etc - which can be difficult to measure.
I am not making excuses for the appraiser--it is very important to get things right. It appears that the difference in sqft did not cause a problem. If you have concerns contact the appraiser for more information. The appraiser's work file will have the sketch and measurements.
Also, read the report for comments on sqft.
I replaced my measuring tape years ago with a laser --sure helps in measuring those hard to reach spaces . The laser is connected to my iPad with an app that draws out the plan. I make sure everything is correct before leaving the property.