"So" is a good way to start a question when it's on a new topic. In the example above, the speakers were just introducing themselves and making small talk. The word "so" shifts the conversation into discussing why the new person moved to that office.
Here are some other examples of "so" used to start a conversation or introduce a new topic:
(someone) was transferred (to somewhere)
To "be transferred" means that you are sent to work in a new department or location. For example, if you work at an office in San Francisco, but your boss asks you to go work in the Atlanta office instead, you can describe it by saying:
I was transferred from San Francisco to the Atlanta office.
Being transferred usually means moving from one city to another while working for the same company or organization. People in the military especially get transferred a lot. But sometimes it can mean moving from one department to another while staying in the same office:
She was transferred to Central Production.
And there's also the case of athletes. When they're "transferred", it means that they have to go to play for a whole new team.
Being transferred is a decision that's made by a person's bosses. If you ask to move to a new office or department, you can say that you got a transfer.