I would also have given a 5*. This is an excellent lot that can be used for trading on this site when you don't collect mint stamps yourself. Getting material that you can actually pass on to someone else is very rare and always worth 5* in opinion.
I also put 3 points when I got less stamps than required by the rules. Anyone can put at least 5 or even 10 stars - this is a personal matter for everyone.
But nobody can put pressure on a person if he(she) simply asks to follow the rules, IMHO.