Without information of how you are slicing this measure I can’t confirm.
But if you were to put this measure in a matrix, with product name on rows, you will get same value as Total Sales for each product and not the information regarding top 3 products.
I would use something like this:
removing Total Sales:
If you have any questions on KEEPFILTERS, here is a post from @BrianJ Thinking Behind Use of KEEPFILTERS