The red route is a required segment. Each rider checks into the control, then goes off and does the segment (which is a secondary checkpoint e.g. CP3b) and comes back through the main checkpoint (but not needing to stop again) and then off they go on their chosen route towards the next checkpoint.
I'm watching Frank on Trackleaders - definitely hasn't reach CP3 yet. The
Controls spreadsheet on Free Route has had a number of anomalies so I wouldn't rely on that one for that particular piece of data. The FR "brevet card" is correct though (
http://www.frrt.org/tcrno4/r/155-frank).