The 'singer' involved had both poor diction and enunciation
The song that I believe you are talking about is Sexy Can I? by Ray J. The singer sounds like they are saying Nick Cannon but in reality they are saying Sexy Can I?
No, she is not. She is a full fledged singer...however, sometimes she doesn't sing ALL the lyrics to every performance due to her dance moves and other performing acts.
Find the lyrics online and listen to the song while reading the lyrics. That's how I get a better understanding of what they are saying. You can understand some better than others, it just depends on the vocal training of the singer.
Sweet Child o' Mine is the music video that the singer has the lyrics on his guitar.
If its not on Lyrics, then its Improvisational, called Improvising.. can sometimes happen when things are screwed up.
One can find the lyrics to Subway Song by Austin Mahone on Lyrics Freak and Lyrics Mode. Sometimes users upload fan videos on You Tube with the lyrics added. Austin Mahone is an American Pop Singer who became popular due to viral videos of his performances in 2011. He was born in Texas in 1996.
Most of the lyrics (if not all) are by the lead singer Wayne Coyne.
Lyrics are for the singer to sing, and most of the time (unless they are a pop singer like Rihanna), they write their own songs so it expresses their feelings as well.
Singer performs; author writes the lyrics and/or the sheet music.
A person may find the lyrics to the song "Tu" by the Colombian singer Shakira at "Metro Lyrics". The English translation of the lyrics may be found on "Lyrics Translate".
There are many places that one could find lyrics to 'Have You Ever' by the singer Brandy. One could search websites like Metro Lyrics. Lyrics 123, AZ Lyrics, or Lyrics.
They write their own songs. Caleb Followill, the lead singer writes the majority of lyrics but his bandmates, Nathan, Matthew and Jared Followill help him with them sometimes.