Surveyors are engaged by many people and organisations for varying purposes. Perhaps a neighbour wants to establish their property border in order to place a fence on its correct line.
Whilst a surveyor generally can’t come onto your land without your permission, someone would have engaged these people and given them permission (rightly or wrongly)
It’s up to the person or organization that engaged these surveyors to pay them. If your strata say they didn’t engage them, then someone else will pay.
Maybe you are reading too much into this event.