I personally would not read too much in to this.
I just take it to mean for example if you are given 25k in BU institutional aid freshman year, you will get $25 all 4 years.
Does it mean you may pay more year? Absolutely yes, simply based on the following premises:
BU does not guarantee to meet 100% demonstrated need.
Your child’s federal loan amount will change each year based on your students ability to borrow more
$5500 freshman year
$6500 sophomore year
$7500 junior senior year
There will be increases in tuition (calculate between 3 & 5% each year), on face it seems like you will not get increased grant aid in proportion to the increases each year.
Your EFC will change every year based on fluctuations on your family’s income and assets.
ETA: you need to ask BU clarifying questions about how the policy will affect your family.