One thing I am learning in Intermediate Greek, is that the Aorist can have a continuing action to it. However, that might be better seen as part of the "undefined" aspect of the Aorist.
I think for this verse, you can trust OH's parsing of this participle. This is a verse we actually studied in Greek, and "was preached" is what we were told was the best way to translate it. I wanted to use "preaching" but it doesn't bring out the Aorist aspect enough.