Good catch.
NTDP U18 roster shows Middendorf as uncommitted.
DU currently has 6 NLI's signed for 2018-19 (4 forwards and 2 D-men) and just got a verbal from USHL's leading goalie, Filip Larsson. Plus 3 other recruits who were originally slotted for this season.
Current roster has 4 seniors (Junda, Jaillet, Plant and Hammond) and 3 pretty much expected to leave early (Borgstrom, Gambrell and Terry). That is 4 forwards, 2-D-men and 1 Goalie.
Either DU asked Middendorf to wait a year/ no scholarship money available or he and his "family adviser" decided that chances were not good for a scholie/didn't want to wait until 2019-2020 and this would be a good time to reopen recruitment . Since DU can't talk about recruits until NLI is signed there has been no public announcement.