No it's not. When it was offered, before THIS season, Butler had only played 2 years in the NFL. He still was under contract for 2016 for league minimum, plus he was facing a 4th year as a RFA and then a possible 5th year under the franchise tag. So over the three years - 2016, 2017, 2018, he would, at most, if the Pats played it out like they could, make about $18.5 million. None of that, at the time the Patriots made the offer, would have been guaranteed. And then in 2019, if everything broke right for him, he could make a bigger payday, maybe along the lines of $16 million in 2019 as a UFA.
The Patriots offered 4/28, which means, assuming it was spread out evenly, that over the first three years (2016, 2017, 2018), he'd have made $21 million, instead of the $18.5 million that he could have made in the current system. And a bunch of that would have been guaranteed. Then in 2019 he'd have made less than in the current system - if everything broke right - and then he'd be free to roll in huge money.