My issue was that
cat volcanoes.txt | wc > islands.txt and cat volcanoes.txt | wc | cat > islands.txt
both perform the same function, rewriting the islands.txt file with the output of
cat volcanoes.txt | wc
The point of the lesson was to show how you can pipe a series of command outputs into sequential command inputs on one command line, but the way the do it (output of cat into wc, then output of wc into cat) appears redundant, and I think the lesson would be clearer if the second pipe moved the output of wc into a different command.