Yes, rectangles with horizontal lines through them are how the chart shows that a particular pair of contacts are closed, and blank rectangles are how it shows that they are open.
The entire chart is also divided into sections for different cycles — you can see those along the top of the chart. During the entire regular cycle, cam 6 16-13 is never shown closed. Cam 8 16-13 is shown closed at a couple points. From that, we can tell that cam 8 is what we’re interested in looking at for our troubleshooting.