This is an Avianca ticket, but the restrictions in this case are similar for the fare (PEX00RIQ, "econo")
Category 15: Sales restrictions
TICKETS MAY ONLY BE SOLD IN PERU.
NOTE -
PROMOTION--APPLIES FOR PERUVIAN RESIDENTS--
RESIDENCE IN PERU SHALL BE ACCREDITED WITH
PERUVIAN ID OR ALIEN CARD OTHERWISE AN
ADDITIONAL
CHARGE OF USD 178.5 WILL BE APPLIED OR BOARDING
WILL BE DENIED.
///
Google flights doesn't issue tickets directly... if you followed the link from Google Flights and booked directly on the Avianca website, you are correct, it isn't mentioned. What I understand happens is that when you access the Avianca website from its main page and then indicate the search parameters, a pop up message will indicate that SUPERPROMO and ECONO fares on certain domestic routes are for residents only.
Ten presente
En las siguientes rutas, las opciones tarifarias Súper Promo y Econo solo aplican para residentes en Perú acreditados con DNI o carné de extranjería:
Entre Lima, Cusco y Puerto Maldonado.
Entre Lima y Juliaca.
De no acreditar la residencia, debes pagar en el aeropuerto un cargo de USD 178,5 (IGV incluido). Si incumples estas condiciones, el abordaje podrá ser denegado.
When you access the site from the GOOGLE FLIGHTS link, you are directed to the search and you never get to see that pop-up message... Nevertheless, the fare restriction exists...