A couple of things not as needed here.
One is that you subscribe to the QueryCellStyleInfo event after you have called ResizeToFit so there would be no way for the grid to know that it needed to adjust for a bitmap in the resizetofit call.
But even subscribing to the event before calling resizetofit is not sufficient as the GridRangeInfo.Table will only catch the visible rows. So, as long as the node is collapsed, it will not really use teh QueryCellStyleInfo event which is what is needed to know about teh image.
One solution is to call resizetofit as you expand a node. You could always do it, or you could keep track of what tables have already been sized, and only do it on the first expansion.
void gridGroupingControl1_GroupExpanded(object sender, GroupEventArgs e)
{
GridTableModel model = gridGroupingControl1.GetTableModel(e.Group.Records[0].ParentTableDescriptor.Name);
model.ColWidths.ResizeToFit(GridRangeInfo.Table(), GridResizeToFitOptions.IncludeHeaders | GridResizeToFitOptions.IncludeCellsWithinCoveredRange);
}