Who knows what motivates a person, but strictly from an opportunity perspective, Twitter is a more certain outcome than Square. If NFC on the phone takes off, then Square technology may soon become antiquated.
This move certainly doesn't bode well for Square, though.
It's important to note that most of what Square brings to the table is not hardware. It acquires merchant transactions and manages payment risk. Square can simply support other hardware technology, but their focus is on the merchant side.
This move certainly doesn't bode well for Square, though.