curiosity in default column header

[Rob Sargent <robjsargent@xxxxxxxxx>]

    riftehr=> select
      ascii(substring('sadb', 2,1));
       ascii 
      -------
          97
      (1 row)
    
    riftehr=> select 24::bit(8);
           bit    
        ----------
         00011000
        (1 row)
        
      riftehr=> select ascii(substring('sadb', 2,1))::bit(8);
        ascii   
      ----------
       01100001
      (1 row)
      
      Why is the last one headed "ascii" and not "bit"?