If a flying creature is knocked prone, has its speed reduced to 0, or is otherwise deprived of the ability to move, the creature falls, unless it has the ability to hover or it is being held aloft by magic, such as the fly spell.
All the winged option for the Variant Tiefling states is
Winged. You have bat-like wings sprouting from your shoulder blades. You have a flying speed of 30 feet while you aren’t wearing heavy armor. This trait replaces the Infernal Legacy trait.
From this question we know a PC can stay in place in air. However, since nothing states it has to keep moving to continue to fly, is it considered to have the hover ability? Specifically, if it is knocked prone will it fall or not?