An elected official attending and participating in an event sponsored by a community organization is not the same as the expendature of government money on proselytization for a particular religion.
You've got a point. But I really doubt that anyone has "met Jesus" while walking past the City & County building during December. Proselytizing is an active sort of business.
But if we say no public money for any religious-related display, we are going to be poorer as a culture. "Merry Christmas" is a Christian greeting to those of us who are but it's a traditional seasonal greeting to those of us who aren't.