Made on the computer, but samples (sounds used for making the music) like the guitar probably comes from a real person, then modified to make it synthesize-able.
Especially because these music are XM (Fast Tracker) and IT (Impulse Tracker) modules. It was made with a tracker (Tracking, in terms of music, is a way of making music, very popular in the first games, all consoles (Maybe not the newest ones, like since PlayStation 1) utilized this method. It is still quite popular and more advanced then it was at old days.).