In these situations most Newbies become prey of FOMO and lose most of their capital. They think it has Hit an ATH and will go for a Pullback and they Short. But it continues to Rise higher.
Your title asks about the actions of newbie holders and then you say that these newbies short bitcoin, so what are they really? Are they holders or traders? Who are we talking about. I'm a holder and I know a few holders who are in this space for 5-10 years and none of them has ever shorted bitcoin. If you do, that makes you a trader, more of a speculator than investor. After all, you're betting money on a selloff.
What should holders do? Keep holding. They can always do like me - celebrate the ATH by treating themselves to that new thing they wanted to buy but couldn't find money to do so. Maybe it's a swimming pool in their back yard, maybe it's a new bicycle, maybe a new computer, or family trip to some tropical island. I don't know what you guys like but when bitcoin hit a new high in 2017 I remember I bought myself a gaming PC because I was into it at the time.