It could be that the song has a special meaning for him or it was requested for a particular event. Also, it might be part of a performance or a way to express his emotions.
Maybe he just loves the song and wants to show his singing skills.
Maybe he's in a musical or just having fun expressing himself through singing.
Maybe he has a crush on her and wants to express his feelings.
Maybe the fat boy is in a good mood and wants to express his happiness through singing.
The cartoon boy could be singing about his dreams and aspirations. Or perhaps it's a song about friendship and kindness. It really depends on the context of the cartoon.
There are many cartoons like that. For example, in some musical-themed cartoons, a boy might be singing to express his feelings or tell a story.
The coloring of a singing boy cartoon might have bright and lively colors to show his energy and joy. Also, it could have detailed shading to add depth and make the image look more realistic.
It could be a musical number where the boy showcases his talent or a part of a story to convey his emotions.
It might be that he's inspired by cartoons and wants to recreate the magic of the song in that style. Or, it could be part of a creative project or a way to express his creativity and unique style.
It could be a musical cartoon where they perform on stage together.
It's hard to tell for sure. Maybe the character's appearance and voice don't provide clear indications.