Английский. Очень важно

"Rang" - потому что это действие в прошлом, а не дождь. "Was raining" - про дождь, а тут - звонок.

Why "Rang" is Correct
You are absolutely right that the sentence refers to a specific moment in the past (1 o'clock yesterday). However, the key to understanding why we use "rang" and not "was ringing" lies in the nature of the action.
"Ring" is a punctual verb: This means it describes an action that is completed in a single moment, like a sudden event. Other examples of punctual verbs include "arrive," "jump," "kick," etc.
"Was ringing" is the past continuous (progressive) tense: This tense describes an action that was ongoing or in progress at a specific time in the past.
Therefore, even though the sentence refers to a specific time, the action of "ringing" happened instantaneously at that time. He didn't spend a duration of time ringing; it was a single, completed action. Hence, we use the past simple "rang."
Here's an example to illustrate the difference:
"He was ringing me at 1 o'clock yesterday, but I missed the call." (The action was ongoing – he was in the process of ringing when the call was missed.)
"He rang me at 1 o'clock yesterday, and we talked for an hour." (The action was completed – he rang, the call connected, and then a new action (talking) began.)

не было длительного действия

не "was raining", а "was ringing".
теперь к самой сути: если бы ты сказала "was ringing", то был бы акцент на том факте, что он звонил тебе именно в тот конкретный момент, в ту минуту и в ту секунду. у тебя вместо этого вообще указан час. он ведь не стал бы сидеть на линии звонка целый час, правда? здесь же тебе нужен только сам факт того, что тебе позвонили в какой-то момент (в какой конкретно - не важно) в 1 o'clock.
я это так понял, надеюсь не ошибся.