Starbucks has never really been "Pro-Gun," they just have never been "Anti-Gun" either. They've tried to remain neutral on the whole issue, simply stating they would follow local laws regarding open-carry of firearms.
Over the years their stores have been used as a meeting place and have unwantingly hosted rallies and open carry displays, along with anti-gun protesters loudly crying about their stance, or lack thereof.
They have once again made a noncommittal request for gun owners to not openly display firearms in their stores (but if you do, we'll still serve you... just try not to, ok?)
I can't say I blame them, they've spent a few years under somewhat intense scrutiny from the Antis, and an unwanted embrace from the Pros; all because they have tried their hardest to not pick sides.