It is (was?) a click bait headline.

The Highway Code doesn't have the force of law. If something in it says "you should do X", its a recommendation. If you don't do it, it won't look good if you're in a crash and might contribute to a dangerous driving charge, but it's not outright illegal.

If it says you "must not do X", then it it something illegal. However, it's not the Highway Code that makes it illegal, there's genuine legislation that the Highway Code is paraphrasing.

The article doesn't bother to say which it is.