I read the page and I have to say that it could be worded better. It says it’s not restrictive, and you can apply to other non restrictive schools as well as RD, so they are suggesting that you can’t apply to ED or REA, but if they care, they should spell it out
FLEXIBILITY
Early Action applicants may apply to other colleges through regular decision and other non-restrictive early action plans. Admitted students can accept the offer of admission on or before the May 1 National Reply Deadline.