Here's the way it works. He's an exclusive-rights FA this year, meaning the Bills own him, period. The next year he's a RFA, but since he was undrafted, if the Bills give him the minimum tender, another team can sign him and the Bills have the right to match the contract. If they give him $1M+, they can make him worth a 3rd rounder or higher. And depending on what was offered to him, he was probably smart to refuse a lowball offer and wait to see how he developed, trying to score the big bucks later-on.