The video quota only takes into account the size of <x id="START_TAG_STRONG" ctype="x-strong" equiv-text="<strong>"/>uploaded<x id="CLOSE_TAG_STRONG" ctype="x-strong" equiv-text="</strong>"/> videos, not transcoded files or user export archives (which may contain video files).
The worst-case scenario of an average person spying on their friends is quite unlikely. There are much more effective ways to get that kind of information.
This is an <x id="START_TAG_STRONG" ctype="x-strong" equiv-text="<strong>"/>import<x id="CLOSE_TAG_STRONG" ctype="x-strong" equiv-text="</strong>"/> tool and not a migration tool. It's the reason why data (like channels or videos) is duplicated and not moved from your previous PeerTube website.
This is just an extra information injected in PeerTube HTML that is required by Twitter/X. If you don't have a Twitter/X account, just leave the default value.