The Halo related scene starts at 19:07. The guy gets kitted out holographically in an MC-style suit and someone selects a weapon for him from a holodeck menu. The graphic on the menu appears to be based on the MA5C assault rifle from H3 (although that's visually very similar to the MA5B from H1), but when we then see the suited guy he's instead got something reminiscent of a battle rifle. Quite a mismatch there - I wonder why. Maybe the animators tried drawing the AR and found it problematic?

Weapon firing occurs at 20:54 - a generic zap. The weapon is subsequently changed to a 'freeze ray'. In the cropped image you don't see much of that, but it doesn't remind me of anything from Halo.