I think this whole think is much ado about nothing. Being Jewish is not only following religion and traditions but it is also what you feel in your heart. To many Jews the second day of Rosh Hashanah is not as important as the first day and I’m sure if you really wanted to go, to this charitable event, you would have been forgiven. After all, quite a few Jewish actors participating in the flea market because they probably felt the mitzvah was also important. It is obvious that the scheduling of this event was not intended to be on a Jewish Holiday. So if you felt you had to miss this flea market, there will be one next year. Live and be well!
"The secret of life is to appreciate the pleasure of being terribly, terribly deceived".
Oscar Wilde, A Woman of No Importance, Act 3