Using eBird's "Explore" by species I found reports of the Magnificent Frigatebird in the Portland and Lyle areas. Based on that I would not consider your report worthy of being rejected - it seems to be an "unlikely". However, not having a photo or some other evidence may have been the reason.
All,
I have found that eBird is geared to accept the reports of some people (do they have a "user rating"?) much more readily than others. This is not bad or wrong - it's a good thing because none of us wants just anybody to be able to report something rare (or even unlikely) - the quality of the database -has- to take precedence over the feelings of the users.
Having said the above - I once had a report I made of a Great Egret at Ship Harbor rejected. Since my report was just one of -many- that were made that day and week for that same location (same bird?) ... I have never understood why "mine" was rejected when others were accepted ... it seemed/seems kind of arbitrary (to me). Still does. - Jim