Yes that's how it works. The S in the circle on the left side indicates whether a forum will be shown in all searches by default (view new posts, view last days posts, and default searches). If it's a grey circle that forum will be shown, if it's a red circle that forum will not be shown - just click on the circle to change it's status. These are the forums you currently have set to not show on searches by default:
2nd gen no engine
24v
12v
1st gen
1st gen support for discontinued
1st time owners
conversions
general diesel
chapters & events
rigs spotted
competition forum
other
politics