The article does contain an error here, for the code point on the page is actually U+FFFD, not U+D83D (which of course is unrepresentable there). I trusted that (being a little surprised that it’d do the replacement, which is more what I’d expect of Python, but accepting it all the same) and didn’t pull out an old browser to confirm what actually happens, which is, as you say, an unpaired surrogate code point.

The article should probably say '"\ud83d"' instead of '"�"' (even though the number of backslashes still then requires thought), because yielding U+FFFD there would be a completely valid (and preferable, in my opinion) solution.