Certainly not all the language statements affect the control flow directly. The statements which do not affect it could be drawn as code blocks. Why blocks but not just individual statements? Well, developers tend to group statements into chunks which help to understand the code for the future readers. The chunks are separated from each other with blank lines. This fact should be respected on a flowchart diagram. As for the shape, a plain rectangle seems to be a very reasonable graphics primitive for a code block. The examples on the slide show a single code block and a couple of blocks one after another with the only difference in the code of a blank line between the statements.