Use of written Chinese in spoken context
Hong Kong officially uses Standard Written Chinese as the written language, but in reality all shades of writing fall on the Saam kap dai spectrum, which combines Classical Chinese, Standard Written Chinese, and Written Cantonese into one piece of writing.

The relative proportions of those styles are changed depending on the tone the author wishes to set. Increased use of Classical expressions variously give off a literary/archaic/learned impression, increased use of Standard Written Chinese give off a proper/stiff/formal/serious impression, and increased use of Written Cantonese give off a casual/informal/relaxed impression. For example,


News items may largely use Standard Written Chinese but occasionally inject a few Cantonese expressions;
Gossip magazines will largely use Written Cantonese but occasionally inject expressions from Standard Written Chinese and/or Literary Chinese


Song lyrics are written first then sung exactly how they are written, not spoken on-the-fly, so it is probably worth looking at it from a saam kap dai spectrum point of view.