Unless the pot odds were correct generally only fish raise all-in on the turn, especially if this ends up being an over-bet. Given the opponent had possibly --9 Hearts, 2 9's and 3 Kings as outs (Kings were not outs since you had one, but opponent did not know this), the pot odds could have been in their favor to call.
Without all of this information it is difficult to justify the other person's rationale with just one screenshot.