Hi Manson, an interesting thread.
These days when looking at the origins for rare birds, we usually go first to the Backward Trajectory Maps produced by HKO (on their website, under the heading 'Weather Monitoring Imagery'). You can quickly scan through the daily images for July under 'Past Backward Trajectory Map'.
There is nothing here for to suggest a wind assisted northern origin for these recent arrivals, all the daily trajectories for July are coming from the south, as you would expect at this time of year. I think as Captain says, wandering immature birds is a more likely explanation, that is assuming they are all wild birds which they may not be.
