It seems this 4:3 resolution device could be an iPad Mini 2 or later (including iPad Mini 3, iPad Mini 4). I would like to know if your device is similar to the iPad Mini 2 or later, or if you have any other Apple devices capable of playing BTD6.
Hmm... The screenshots on that page are definitely not from an iPad Mini 2, as the resolution for iPad Mini 2 is at 2,048 × 1,536, rather than 2,732 × 2,048 as this screenshot has. These screenshots were probably from an 12.93-inch iPad Pro or something like that.
Likewise, this screenshot of Version 6.0 Military MK is from a 1,920 × 1,604 device. Not sure what devices use 1920 x 1604 though. But I see a pattern - all these devices are pretty similar in aspect ratio when simplified down to lowest common denominator ratios.