The fact that it is a Motorola device is pretty easy to note, because the filing is directly attributed to Motorola. The reason why we believe it to be either the Moto X+1 or Moto X Play is because of the dimensions listed in the filing, which show the device height to be 140 mm (5.51-inches), the width is 72.6 mm (2.86-inches), which are dimensions a bit smaller than the LG G2, which is a 5.2-inch device. Given that, we can't imagine this device is any larger than 5.2-inches, meaning it has to either be the Moto X+1 or the Moto X Play. The X+1 is expected to be announced next week, so that makes the most sense.
The FCC filing only covers the AT&T and T-Mobile cellular spectrum, so there are still a couple more variants of the Moto X+1 to expect in regulatory filings.