That MIDI file has standard pitch bends in it (you can hear the notes changing pitch while they are audible) however it sounds extremely off-key. It seems like the creator of the MIDI file did not set the range of the pitch bends properly, or used a program that had them set incorrectly. The result is that when the pitch bend is set to (for example) +1000, the intention was to go +1 semitone but the result is that only +0.5 semitones is heard, or something along those lines.
I would have to look a bit more closely to confirm this, but at quick glance it looks like a mistake in the MIDI file, assuming the pitch bend range is larger or smaller than it actually is without actually setting it to a specific range.