Spark 1080x1920 (IG Story) size is downloading at 720x1280px

When I download a Spark Instagram Story-sized MP4, 1080x1920, it shows as 720x1280 px to my client and they think I am giving them the incorrect size. 

Also, the 1080x1080 MP4 downloads as 1280x1280. Very odd.

Does anyone know why this happens? I need to give my client a reason.

Thanks!