真的那間選角公司
字面的一層：真的有這樣一個地方在做這件事。
noun · C1
A company or office whose job is to find actors for the small parts in films, television programmes and plays.
（電影的）臨時演員選角公司
核心畫面
Picture one office with a very long list of actors. A film calls and says: send us a bank manager, two nurses and a taxi driver. The office does not send interesting people; it sends the ones who look the part, because that is what the film asked for. Everything this expression does comes from that office and the kind of person it sends.
「可以想成一間辦公室，手上有一份很長的演員名單。劇組打電話來說：給我一個銀行經理、兩個護士、一個計程車司機。這間辦公…更多收起
「可以想成一間辦公室，手上有一份很長的演員名單。劇組打電話來說：給我一個銀行經理、兩個護士、一個計程車司機。這間辦公室不會挑有趣的人。它挑的是「看起來最像」的那一個，因為劇組要的就是這個。這個說法後來的所有用法，都是從這間辦公室和它送來的那種人長出來的。」From the word’s history
The name began as a trademark — Central Casting, a real company supplying actors for small parts — and then became an ordinary noun for the work in general.
「這個名字本來是一家公司的商標：Central Casting，專門提供小角色的演員。用的人多了，它就變成一般名詞，可以泛指這一行，也可以拿來開玩笑說某人「像被挑來演的」。」
Wiktionary entry for central casting, supplied in this packet (source_ref kaikki:3f6f69a190036ae4:2771417318): a trademark genericization, from the brand name Central Casting.
Two branches
像被挑來演的那種樣子
把辦公室送來的那種「太符合想像」的人，拿來形容真實世界裡的人。
noun · C1
If you say that someone or something has come from central casting, you mean they look exactly like the standard picture of that type of person or thing, as if an actor had been chosen to play the part.
活像選角公司挑出來的樣板