Baseball is boring. Being a pitcher is worse. Being a reliever on an Arizona Fall League team with a 20-man bullpen leaves you with so much free time, you're probably insane if you don't spend your afternoons swallowing geckos.
The Mets Minor League Blog identifies him as Miles Mikolas of the Padres' double-A affiliate. They're unable to answer the question of whether the lizard was alive before disappearing into the gaping maw of a righty reliever.