Translation:We were contacted by a famous man.
I'm sure it will be explained later on once the grammatical notes are up but basically "bởi" is used when we want to place the agent (the actual doer of the action) after the verb rather than immediately after được or bị? Does it sound more natural that way compared to chúng tôi đã được một người đàn ông nổi tiếng liên hệ? I suppose it helps making the sentence clearer especially when the agent is a group of word.
We have two ways to make a passive voice in Vietnamese. The first one has the same structure as the official sentence above. The latter is like the sentence you supposed.
In daily conversations, if we need to make a passive voice, we prefer using the structure as you said: Chúng tôi đã được một người đàn ông nổi tiếng liên hệ.