The first line is related to the week ending on February 2nd, so Sales Amount includes only 2 days (February 1st and 2nd) excluding the amount of other 5 days in the same week (January 27th to 31st). The same happens in the last week, which includes June 29th and 30th but does not include sales for the remaining 5 days in the same week (July 1st to 5th). This also explains why the report includes a week ending in July 2008 even though the Month slicer only includes dates up to June 2018.
We can create a measure that removes incomplete weeks from the calculation, as shown in the following code. A similar technique could be used for incomplete months and quarters.
There are some interesting techniques that Marco shows off, including hiding incomplete weeks.