But a diary will have mental impressions and context that is missing from smartphone GPS records. E.g. a smartphone might tell you that someone attended a radical anarchists' meeting, but a diary will likely reveal what was said in that meeting and the author's mental impressions.
Remember the question we are discussing: could people in 1789 have anticipated the kind of invasions of privacy searches of smartphones enable today? Given the kind of detailed records some people back then kept, not just bland metadata but detailed accountings of their thoughts, I think the answer is "yes."
We are still a long way from smartphones automatically capturing the kind of private thoughts people choose to write down (back then as now).