The Packers extended ERFA tenders to Allison, Donatello Brown, Callahan, Michael Clark, Kerridge, McCray, Pankey, Patrick, and Whitehead just before the start of the league year, but one name, Herb Waters, was conspicuously absent. The reason Green Bay did that, unsurprisingly, is money and also because they could. Green Bay also did not send a tender to LS Taylor Peppers, but it appears they simply do not want him.
Under the CBA teams can indeed sign a player for less than the NFL rookie minimum of $480K if they are not on an Active/Inactive list when signed. Since Waters was still technically under contract while he was on the IR list, Green Bay had to wait until the first day of the new league year when his status changed to being a Free Agent to sign Waters.