Hello sajha gurus, I need your help specially if you work in HR.

I recently had a 3 round interview for a company, and after 4 weeks I got a reply saying the position is filled in the IT team that I interviewed for. But they want to interview me again for another team. What does this signal to? What are my chances?
I have an offer from another company B for which I have a deadline to accept the offer. I really like the 1st company, but I am not sure if dropping an offer from another company would be a good decision. Please suggest !