Two people leave the same room, walk down the stairs without a word, and part at the door. Then comes the twist: the boy says out loud that he wishes people would talk to him, and a girl twenty metres behind him is wishing exactly the same thing. They were close enough to have spoken, and neither did.
The poem is quietly sad, and a little frustrating. The speaker watches from outside, with the line "little did he know" sounding almost like a narrator shaking their head. The plain, short lines and the repeated "in silence" make the quiet feel heavy and almost deliberate, as if the silence is a habit they both fall into.
What stays with you is the irony. Loneliness here isn't about being alone, because these two were together. It's about both people waiting for the other to make the first move. The poem leaves us wondering how different things might have been with a single "hello."