I've seen pictures of 6-wheeled and 8- wheeled vehicles similar to this. I believe they were amphibious. The one in the article, however, could probably travel faster over water.
That would be an Argo. They've been around since the 60s. Canadian made, not too far from where I grew up. They are slower in the water when using the wheels as paddles, but they have a mount for an outboard motor. Not quite as smoothly amphibious as the 4-wheeler though.
A number of companies marketed similar vehicles in the 60s and 70s. The Banana Splits used an Amphicat.