Picture a lane so full that nobody can walk straight. Shoulders touch shoulders; to move at all you have to turn sideways and push. Throng can be thought of as that pressing itself — not just many people in a place, but people packed until they press on each other. Everything else the word does comes from looking at that same picture from a different side: the mass as a thing (a throng), the bodies arriving (people throng the square), the place after they arrive (thronged with ), and, in writing, things or animals packed the same way.
The source entry traces throng to Old English þrang / ġeþrang (crowd, press, tumult), from a Germanic root meaning pressing or narrow, and compares German Drang (a pushing force) and Gedränge (a throng). So the pressing in the modern word is not a reading we added to it; it is what the older word named.
來源資料把 throng 追到古英文的 þrang / ġeþrang，意思是「人群、擠壓、騷動」，再往上是日耳曼語裡表示「壓、窄」的字根，同源的還有德文 Drang（推擠的力量）和 Gedränge（人群）。所以今天這個字裡的「擠」，本來就是它最早在講的東西。
Wiktionary etymology supplied in this packet (source_ref kaikki:3f6f69a190036ae4:1051531982:22053)
Two branches
那一團擠在一起的人（名詞）
這一支是直接把核心畫面命名。你不是在描述誰在做什麼，而是指著那一整團擠在一起的東西說「那個」。所以它是可數名詞，可以說 a throng、throngs，也可以說 in the throng（你人就在那團裡面）。
noun · C1
A very large group of people gathered or moving in one place, packed so closely together that they press against each other.
一大群人
往那裡擠過去、被擠滿（動詞）
這一支是讓核心畫面動起來。名詞看到的是「已經擠成一團」，動詞看到的是「正在擠進來」，以及擠完以後那個地方的狀態。所以它們講的是同一件事的前後兩格。
verb · C1
If people throng a place, or throng into, to, or around it, they go there in very large numbers, so that the place becomes full of them.
湧入；擠滿