Uh… this dog does not code as ‘excited’ here. This dog looks aroused and interested but also anxious and unable to settle.
The very first thing you see is a lip-lick - a very common sign of low level discomfort in dogs - as the tegu is moved towards the pupper. His tail is wagging but his body language is low to the ground and with his weight shifted away from the dog, with ears slightly back (it’s hard to see if there’s facial tension under the fur). Remember, a wagging tail is a sign of emotional arousal and does not always mean a dog is happy. He leans forward to sniff, then draws back and lip-licks again. Every time the tegu is moved towards him, the dog leans further back.
It then cuts to where the dog is standing on the bed - again, with about as much distance as is possible on the bed between the dog and the lizard - but leaning into investigate. His weight is still back and away from the tegu. He gets a tongue-flick and immediately looks away and lip-licks again. There’s a little bit more investigative behavior in which you see immediate appeasement behavior: he sniffs, looks pointedly away and lip licks. The dog then does a full shake-off, another distancing behavior that relives some internal tension in dogs.
There’s then a cut to where the human is coaxing the dog over towards the tegu. The dog is moving sideways along her body with his weight away from the lizard - he appears to be trying to interact with the human without getting near the animal she’s holding. As he gets closer his body is low to the bed and tense, which is not the posture of a comfortable dog, even one moving on a bed and attempting to solicit attention.
This looks like a dog that is nervous about the lizard yet still trying to interact with the human. There’s minor investigative behavior, but the dog’s entire body language is very indicative that it would rather not get near the tegu.
I don’t think this is necessarily a bad interaction - the pupper doesn’t appear to be afraid or over-aroused in a way that could endanger the lizard - but its super misrepresentative to portray it as a happily investigative dog.