Um, I think you might have misinterpreted the chart.
Some seat tubes are externally butted - that way you can get the thickness you need around the seat - top tube joint for strength, and the seat post itself is supported via contact to the inner diameter for its full length. Best way to verify is to measure the ID of the tube.
You don't want to go too close to the transition zone on the butting in case you compromise the strength. That's why they give you a 245mm plain wall thickness to work with, you can change the seat tube length by up to 165mm without breaching their guidelines.
The red circle just lets you know which end is which - on an externally butted tube you can also tell because you can actually feel the transition on the external butt.