"==" is an expression, or a test so will return either true, or false depending on if the test comes back as true (e.g. 1 == 1 returns true, 1 == 2 returns false)
"=" is setting the value of the field and will return true if it manages to set the value (I have several times put in only a single "=" by mistake and spent a long time wondering why it seemed to be doing somethign when it shouldn't)
As for not working, check what the radio groups are returning as their raw values by using:
xfa.host.messageBox("" +radioGroup1.rawValue );
It might be set to associate the radio's with a numerical value (In the Object > Binding tab).