Or to find him suspicious because of his reaction to hearing sirens approaching?
Yes, but the Oswald defenders say you can't look at the entire context of his actions. Instead, each of his actions have to be considered in isolation and stripped from any context in which he acted. It's like Oswald acting in a giant isolated bubble with nothing going on.
Here, he was just looking at shoes. All of the other incidents around him must not be included.
He just left the TSBD. He just caught a bus. He just caught a cab. He just went to his room. He just walked down the street. He just looked at shoes. He just went into a theater. This is how you're supposed to judge his actions.