A girl in a purple top, baggy pants and sneakers is blowing a kiss, while another girl in black watches.
A girl is blowing a kiss to a boy while someone watches.
A girl blowing a kiss is not assumed to be doing so to a boy.
She can blow the kiss to anyone rather than to a boy
Just because a girl watches another girl blowing a kiss to a boy it does not mean she is the only someone who watches.