Nicholas,
Sounds like you were talking with someone who attends St. Vladimir's, where someone is apparently teaching such things (from what I've read at another forum), and apparently some people are picking such a theory up and running with it.
And technically, even according to these narrow beliefs, ecumenism and modernism are still heresies since they are heresies of an ecclesiological nature, which is directly related to christology and in Orthodox thought inseperable from certain christological beliefs. Just as a discussion about Mary could be christological in nature, so can a discussion about ecumenism and/or modernism.