There's a difference though between synesthesia and using non musical words to describe music.....
"I am very adamant about certain songs being blue or red, or round or sharp, or soft and shimmery. I use non-musical words to describe my music. By adding all the cool sounds and elements of production, it can paint an imagery in someone’s mind.”
Doesn't mean synesthesia.....tons of people describe music that way. Most people on this board do.
I do believe that Lorde has it. The thing that mentioned her having it sounded legitimate and gave real reasoning.