That note about "both signs have been reversed" only applies to the example on the right side, where –4 was distributed into the expression in parentheses.
Notice on the left example, the signs were not reversed.
When you distribute a negative number, that's when the signs will reverse. Since you're distributing a negative number, you'll be multiplying each term in parentheses by a negative number and that negative is what reverses the sign on every term.
So, yes all of the signs will be reversed each time you distribute a negative number into the parentheses, but not if you distribute a positive number.