Ok so this is the Philippines. And it's really not a big deal in many of the restaurants I've been to for people to bring in outside food. I've had friends who even bring in rice and ulam into places like Yellow Cab and Seattle's Best and no one would mind. After all, we don't have such things like the Health Code in the USA that states that a restaurant is responsible if someone gets sick eating in their resto.
Furthermore, this isn't exactly a first world country. A sale is a sale. If I'm gonna buy from you anyway, why would you kick me out just because I'm lugging along some food of my own? I'd understand if the food is a giant pizza, but small food you can eat with your hands shouldn't be a problem.
Also, as far as I'm concerned, as long as you're not a hotel or one of those fine dining sit-down types of places, I wouldn't assume you'd have a NO OUTSIDE FOOD policy. If you're a Spirals or a Yakimix kind of place, then I wouldn't bring baon in since that would look just tacky, with all those plastic bags and food containers.
BUT COME ON. Starbucks (Technohub), we came there thinking it would be just like the Katipunan branch that lets people bring food from McDo, Jollibee, etc. Without a sign to tell people that "Oh we're different and more sosyal, don't bring that sandwhich in here or else we'll kick you out," we were asked to leave just as we were chewing on our meat pocket things from Yellow Cab. Well excuse me, why didn't you tell us that BEFORE we've sat down, unwrapped our food, sipped our Starbucks drinks and started eating? Was that security guard just waiting to make a fool out of us, thinking "Oh, this will be fun I'll kick them out while they have food in their mouths."
If you're gonna have this policy, Starbucks, MAKE IT FRIGGIN' CONSISTENT. Weirdos.