A precinct or voting location located within a city is not necessarily only for people in the city limits...and the county itself has over 30,000 people.
However...unless this polling location / precinct was redrawn to include more of the county residents voting there, this is definitely an irregularity if the spreadsheet is not a typo - as you can also look up the results from 2020 and 2018 and see that the total number of votes listed for Columbia, NH is in line with city’s population numbers. This should warrant further investigation.
Throughout most of New England, counties are wall-to-wall towns. I think the only exception is northern Maine.