My test invite came from Surrey office too but I don't know which office my application is at right now. How did you know yours? Did you call IRCC and find out? The last update I received was test marked complete on Aug 28th. Been waiting since then but I know it's only been two weeks.Did you receive your test invite?
I guess Sydney is the office where all applications are initially submitted for review and then they are distributed across the processing offices in Canada.
Usually you can guess which your visa office is only after you have your test invite or you call IRCC.
For example- My AOR was from Sydney office and test came from SRY (Surrey) office but my application is being processed at Vancouver office.