Not sure this response will be particularly helpful to you, but FYI the same thing happened to me, as I was booked on the exact same flight (AA164/24MAR SFO>JFK connecting to BA176). Specifically, I was booked on the BA codeshare flight number for AA164.

For me, only the SFO>JFK sector was "cancelled". I received an extremely odd email from my corporate travel desk saying something along the lines of "Your flight has been cancelled by the airline. Please let us know if you would like us to rebook you on the same flight". My response was "eh?" followed by "sure" and lo and behold I'm booked on AA164 (not via codeshare this time). I lost my seat choice though...

This happened on Wednesday afternoon, about 3pm Pacific time, so well before OLCI opened.

I came here looking for an explanation, and you've provided one - I didn't notice the flight number had changed from BA to AA after the rebooking until I saw this thread.