Alternatively, you jumped to conclusions and having seen this iguana didn't bother looking for the other one when I visited in Feburary 2018 both species were signposted and present, so it is quite possible the signage for the Rhinoceros Iguana was being replaced/repaired when you visited.
Either way, the mere fact you saw this animal and not the other does not mean the ZTL entry needs to be removed
Oh! As I seeked all the corners of the exhibit and didn't saw any other iguana, and at same time no label for Rhinoceros iguana, I just got to the easiest conclusion. Would be nice if I'm wrong and they still have Guatemalans.
I edited title and description for match with your explanation
