Update: I realized after I did my checking and the last post that the final project does not have code coverage turned on. You get the stripes once you turn on code coverage, but not otherwise and if you notice the stripes are there for every XCTAssert statement. I had not seen this behaviour before but I believe that the striped lines are simply showing lines of code where only part of the code was executed.
If you hover over one of the striped lines, if the test passed, then the part where the condition is would be displayed in green while the error message (which shows only on failure) is shown in red. So these striped lines are for code coverage indicating partial coverage …