JBoss uses multiple threads so it can make use of multiple CPUs (we do it all the time here). In Linux, there is a kernel option that indicates if threads appear as pcoesses or not. It's been a while since I worked with that option so I don't recall what it is off hand.
so your answer is that JBOSS does use multiple CPUs in LINUX by default.
No, that's not what he said.
JBoss uses multiple threads. To illustrate this you could have a look at a thread dump (see the wiki).
The operating system (Windows, Linux, FreeBSD, etc..) will then be able to schedule the threads on as many CPUs as are available.
PeterJ's comment is just how threads appear in the process view (e.g. ps -aux).