From the NCAA rule book posted on the ECAC website:
"Rule 59 - Interference
59.1 Interference - A player shall not interfere with or impede the progress of
an opponent who is not in possession of the puck, deliberately knock a stick
out of an opponent’s hand, prevent a player who has dropped the stick, or
any other piece of equipment, from regaining possession of it or knock or
shoot any abandoned or broken stick or illegal puck or other debris toward
an opposing puck carrier in a manner that could cause the player to be
distracted.
Waving of arms in front of a goalkeeper by an opponent is interference.
PENALTY—Minor.
Note: The last player to touch the puck, other than the goalkeeper, shall
be considered the player in possession. In interpreting this rule, a referee
should make sure which of the players is the one creating the interference
— often it is the action and movement of the attacking player that causes the
interference since the defending players are entitled to stand their ground
or shadow the attacking players. Players of the team in possession shall not
be allowed to run interference for the puck carrier."
I guess the question becomes, who touched the puck last? - as they were considered to be in possession of the puck. Therefore, if Union player had the puck last he was considered in possession and would have been fair game.