It's not fake as in CG or puppet snakes or a set or they dropped a bucket of snakes on an unsuspecting lizard, but video from different times spliced together to present a narrative that isn't what happened. Fake temporally at least. The producer has acknowledged this:
"Unfortunately lizards, snakes and iguanas aren’t good at 'takes'." She continued: "For continuity, it was better to crop the scenes together based off of the two cameras we had at the time to create the best possible scene."
It looks very convincing to me if it is a fake.