You should still be able to call the method (HelloWorld in this case) all the same, the command method attribute is just the acad 'export' of the method for the command stack.
I don't know about vb but maybe a 'Set' is required for a new instance of exo??
Or-
if 'shared' is the same as static, you would need to call hw.HelloWorld, not HW which is what he is trying to create that doesn't exist, the class declaration is 'hw'