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.