Upvote:3
From my personal experience, you do not need a visa to travel to Mexico if you intend to stay there for less than 180 days and You hold the US Visa or evidence of residency.
I visited Mexico in February 2019 and Traveled on Alaska Airlines and Presented the same documents. I ran on the same problem.
Next time use IATA - TimaticWeb2 and print results from both Alaska's Travel doc link
and take it to CSR or call the supervisor; they are accommodating and swift at @AlaskaAir
For a formal response: https://www.alaskaair.com/content/about-us/contact-us/phone-numbers. Tag them with #iFlyAlaska Twitterhandle
https://www.alaskaair.com/content/travel-info/before-your-trip/international-travel-information