Currently I am computing for 2 different projects.
I have a username for WCG, and another for SETI@Home.

Now, how does BOINC stats pull data together and tie it to my account here?

I mean, what I need to do so both projects would appear under my username here?

External stats sites (for the most part) work off the Cross Project ID (CPID). The CPID is based on the email you sign up with. To how your stats sync up, you need to use the same email to create an account on all your BOINC projects. When you enter it, make sure to enter it in all lowercase (or I've been told).