Those are syslog levels, as common across all kinds of systems. If you read
http://en.wikipedia.org/wiki/Syslog you can see debug is the highest available level, and includes things like notice and info - it's not just errors, it's ALL messages output by a program, including those for debugging the program ("I am now going to start something!", "I started something", "I completed that something without errors").
What your screenshot is showing is the proxy process proxying things for people during normal operations.