I think that they were mistaken in what you were trying to do... or didnt know what a chromecast was :P Probably a 1st level tech with no background.
Maybe the App on one platform vs the other, one works with it vs the other? (android vs iOS).
Generally for CASTING.. weither chromecast or airplay, it IS something that needs to be 'enabled' in the app.. that they can set it up to BLOCK.
I know that SHOMI app did not support airplay or chromecast initially.
Some of it, may have to do with LICENSING too. (at least form some things that i have read).
Many of the content owners, dont want people, who havent paid for the content, to view it.
Having the casting option opens it more up to, you taking your device elsewhere, to let a group who havent paid for it, to watch it.
Though i think many have given up on this.. as just the same you could have them over to YOUR Place, where you did pay for it, etc.
Rogers Ignite Xi6, LG 47LV5400 LED TV, Yamaha