Hi Jan,
By your description OutSystemsUI is checking the device type based on width intervals. After opening the clone of OutSystemsUI, the device type is inferred from classes in the HTML. These ones are probably being granted on the width, so the UI can adapt and you'll likely see the same look and feel on phone landscape and on tablet portrait.

In any case, you can check the device via JavaScript by working on the navigation.useragent. The algorithm is available here.
Hope it helps.
Kind Regards,
João