cool things with wheels, since 2006
Language pedant here: It's a 'longjohn' bicycle. A tandem seats two lenghtwise, and has two sets of pedals.But thanks for posting it, I love old bicycles like those.
You're right, the naming of it has been a mess. The source link will show you that it was called a "tricycle". I know that's nonsense... we all know a trike needs 3 wheels. I can see that some people might understand the word tandem to mean two things in line, for example, circus performers on a swing or high wire. I guess that will do, so I let that be.