This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Calling Thread.start does not mean that the thread will start executing right at that moment; the JVM must first decide to switch away from the current thread. I'm not sure what all the factors are that go into that decision, but the length of the remaining byte code (very short in this case) may well be a factor.
In general, you should not rely on setting thread priorities for trying to force scheduling decisions; that may not work the way you expect, or not work at all.