The code he posted isn't actually valid because you can't "orElse" a list. That being said, I would presume it was meant to include a "findFirst". Something like

    list.stream().filter(Objects::nonNull)
        .map(User::getUsername).filter(Objects::nonNull)
        .findFirst(name -> name.contains(searchString))
        .map(name -> “We have found your user: “ + name)
        .orElse(“We haven’t found”);