I think some song lyrics are just unclear anyway. Like this:
Napalm Death - You Suffer (with lyrics !!!) - YouTube
Death metal... and to some extent a lot of metal has unclear lyrics, yet it does fit the music I guess.
Years ago I was vocalist in a band much like the example you posted (but our songs were 3 to 4 minutes, not 20 seconds, heh). Quite often lyrics are unclear, but I found that's quite often because of lousy articulation (which can be hard considering the speed at which some lyrics are bursted out) as well as non-standard word use (since especially with death metal 9 out of 10 bands have lyrics about torture, murder, death and all kinds of nastiness). The more and more I listened to certain bands, I could decypher the lyrics more easily.
I remember people always whining how it sounded like screaming and the lyrics weren't clear. Then, asking my mom if she could transcribe lyrics of any artist she liked to listen (since she was one giving me a bit of heat for my music choice) she couldn't either... and that was a "normal" singing voice in her preferred style of music.
I thik it's a matter of a trained ear to even be able to transcribe lyrics in a lot of cases. Even now, when I listen to some rap music, I sometimes have to either rewind of take a lyricsheet somewhere cause I just went "whut?".
To make it even more interesting, there are a few death metal bands that don't even use lyrics, but just add in grunts and random shrieks so the voice is more of an instrument in a different way than traditionally.
While we're at it; here's a funny video to illustrate lyrics contents. Since spoilerstags are gone on this board I'll put up a warning here.
It's probably NSFW and if you're easily offended by gory lyrics, do not check it out