Actually, the tables sum is correct. This is because the total for a freeform table can either be a "grand total" or a "column sum."
With the dimension that you have in your table, page URL, the people column is telling you how many unique visitors saw each of the URL. It's very possible that one person can see more than one URL in their time on your site. Having the grand total at the top, which is what your number currently is, tells you the total number of people that saw all URLs. So it deduplicates the amount. For example:
Visitor 1
Page A
Page B
Page C
Visitor 2
Page B
Page C
Visitor 3
Page A
Page D
You would end up with a table like this
People
3
Page A 3
Page B 2
Page C 1
Page D 1
If you were to add up all of those rows, you would get 7. But we didn't have 6 people, we only had 3. But each person saw more than one page. Fortunately we don't have to do a lot of complex work to find out the unique amount of people overall - the grand total deduplicates the rows and gives you the unique amount of people hitting your site.