In another chapter to the growing rivalry between the two clubs, Cox brazenly ran into the Giants' warm-up area during a ball-up drill.
The Magpies premiership ruckman pushed an unaware Mumford from behind, before jumping up and running away with the ball.
Mumford - one of the AFL's most imposing ruckmen during his 2008-21 career - and Giants players such as Stephen Coniglio and Callan Ward looked on in bemusement at Cox's antics.
Daniels didn't know about the incident until watching a replay after the Giants' 32-point win on Saturday night, but took full aim at the American.
"Mason likes to say things that get a bit of a headline," Daniels told the Nine Network on Sunday.
"He likes the limelight, but what he did before the game I thought was really bizarre. A bit of carry on.
"I'd like to think we're really humble and hungry as a team.
"To see that wasn't a good look."
Cox was already public enemy No.1 with the Giants after describing their home ground as "a showground for livestock" when the AFL announced it would be starting the 2024 season with four games in NSW and Queensland.
The Giants social media team and Cox traded barbs all summer in the lead-up to the match.
GWS even set-up a petting zoo at Engie Stadium, formerly Giants Stadium, and named it after Cox.
Welcome to the Mason Cox Petting Zoo � pic.twitter.com/r5Z6ATP1j2— GWS GIANTS (@GWSGIANTS) March 9, 2024
The Giants had the last laugh when Cox failed to register a disposal in the first half and finished with just five possessions for the match.
"If you're going to do that you'd want to back it up on the field," Daniels said
"His comments grab media and that's what he wants. We know we're a small base but we love our Giants fans and last night was really special.
"'Mummy' (Mumford) doesn't usually hold back so luckily he did this time."
In a post on his Instagram on Sunday, Cox said there had been "lots of false commentary" surrounding the incident.
"Will explain what actually happened on this weeks (sic) podcast," Cox wrote.
14°C