The events_SUPERVISED.mat file seems redundant, as the result of the supervised spike sorting is already in the event field of the Link to raw file. This is done so any other Brainstorm process can access to the event data in the same way a with other modalities.
Getting the events (after unsupervised and after supervised) can with the line codes below. There is no need to read the individual channel files.
DataMat = in_bst_data('Floyd\@rawytu288c-01\data_0raw_ytu288c-01.mat' , 'F');
events = DataMat.F.events;