...you see benches like this.
Judging by the nut shells decorating the pavement, I'm guessing it was a man and a woman sitting side by side (but not too close). He had more of an appetite. They were leaning forward (otherwise the shells would be to the side of the bench). Perhaps it was rather heavy discussion about their relationship. Perhaps it was a clandestine meeting to discuss how she's going to introduce him to her father.
Maybe it was a father and his daughter. She's telling him of her new love and he's eating his hand off with stress. The sunflower seeds just aren't enough to distract him from the fact that his little girl is growing so fast. Soon she's going to be a woman and have a family of her own. This little girl who used to cry in his arms will now embrace another.
Or maybe it was a pisshead and his dog.
I'm afraid the secret is hidden deep in that pile of shells. I just hope they're both happy wherever they are (and that the salt didn't give them an ulcer).