Fill 'er Up

Hello again Sherry! I have a dumb question. I opened a jazz midi I downloaded to get some ideas on the drum & bass tracks. The guy used 2 tracks for bass, accoustic bass and fretless bass. I guess I can understand the logic there, but the drum line was named "violin" and the instrument shown in the track properties in Composer was violin. I don't get it. The drum track included bass drum, snare and hi-hat. Why and how dey do dat?? Thanks again! Fred W