"That’s why I am writing today with a respectful request that customers no longer bring firearms into our stores or outdoor seating areas."
No mention of whether the firearms are carried openly or concealed.
The context is people using Starbucks as a venue for open-carry. If it's openly carried, other customers notice and may become alarmed. If it's carried concealed, then other customers generally won't notice.
It's all about not scaring the customers, and I can understand and respect his position.