As for why POTUS_SCHEDULE may have drawn attention to the use of that specific video (with a tweet saying it was only an example):
The YouTube description of this video says "President of the United States of America Donald J. Trump traveling in a motorcade in Lowes Island in Potomac Falls near Sterling in Loudoun County, Virginia at 3:15 pm on Saturday, October 28, 2017. "
The first Q post was only 29 minutes later (3:44 pm on October 28, 2017).
Should we look at what POTUS was doing at the start of that particular drive? In any case, the timing – less than a half-hour difference – seems quite interesting, drawing attention to that specific point in time.