Early Decision Postponed

I applied for early decision, and was told that my application consideration would be postponed and considered for regular decision. What does this mean? It doesn’t really sound like I was wait listed. The letter also said I could submit supplementary materials (another rec letter, new test scores, etc.) if I wanted. Should I do that?
What are my chances of actually getting admitted?
ACT: 31
GPA: 3.2 UW, 4 ish W I don’t remember
I did the interview, visit, and used common app
Chicago (Lane Tech high school-- considered “inner-city”) from middle class family

It means you were deferred- your ED application will now be put into the RD pool. I don’t know about Reed in particular, but generally deferred applicants just have the same percent chance as regular applicants. You can send in an email with new materials if there’s anything significant to report (EC accomplishments, test scores, awards), but I’d advise against sending a letter just for the heck of it.

ACT and GPA seem a tad low unless you have Reed-ish hooks, but you were not rejected.