Show me somewhere it says that?
Because it doesn't actually say that anywhere in the NHL rule book. Only that...
A goal shall be scored if the puck is shot into the goal by a player of the defending side. The player of the attacking side who last touched the puck shall be credited with the goal but no assist shall be SECTION 10 – GAME FLOW NATIONAL HOCKEY LEAGUE OFFICIAL RULES 2019-2020 121 awarded. A goal shall be scored if the puck is put into the goal in any other manner by a player of the defending side. The player of the attacking side who last touched the puck shall be credited with the goal and assists may be awarded.
If no one on the attacking side ever touched the puck, I don't think any goal or assist is credited to the attackers. At least, I see no evidence of it.
If you have some, by all means.......