Airport colectivo

Flew in from Mexico City last evening. Asked for two passengers for the colectivo to Zihua. I can't recall for sure what the rate showed, but I believe it was 240 pesos/person. I was charged 475 pesos, (thinking I'd saved 5 pesos), given the ticket and told to ask for "....." outside. A taxi driver answered, and he took us to Centro.
None of the rates match the ones shown on Rob's chart for Airport Ground Transportation, either the colectivo or the taxi rate. I have no idea why we got a taxi, when we requested the colectivo....or why the rate I paid was lower than the posted rate for a taxi, (and, I think, slightly cheaper than the posted rate for the colectivo).