I don't know what the heck it means, cuz I'm not really familiar with Android OS, yet (I've had a WinMo phone the past 4 years).
I just read this article saying that they noticed something in the developers code mentioning the EVO 4G including Froyo. I know this is short for Frozen Yogurt and from what I've read, it has something to do with allowing the phone to run smoother, but maybe someone with more knowledge can explain it:
http://droidedup.com/2010/03/htc-evo-coming-with-froyo/