I've seen her get tipped for that before and it was the same thing. Just a very quick flash that lasted a few seconds. I think it's not necessarily a scam since her menu doesn't promise anything more than a flash. But yeah, it's definitely not something that makes sense to tip for.
To answer your question "Why spend 1k tk for such thing when you can spend 400 for ticket where she showing full face for long time?" The easiest explanation for this is that a lot of big tippers on cam sites are just kinda stupid. I've seen guys tip thousands of tokens for lovense despite the model aiming the cam directly at their pussy showing that they weren't even using lovense at the time. More money than sense with some of these guys.