Yes, marketing speak, because ‘open tubular’ is an oxymoron. A tyre is either a tub or an hp (to avoid the ghastly Americanism of ‘clincher’). What they’re trying to convey is that the tyre is made using a high TPI cotton (or silk) carcasse with a cold fixed tread, like a tubular, but fitted to an open rim with a bead rather than being sown up and glued to the rim.
As Challenge explain it :
Tubulars and open tubulars: Tubular tires are, well, tubular. They are sewn shut around a seamless latex tube, already in a tube shape, and are mounted and glued directly on a rim, rather than around a tube. However, they require a purpose-made tubular rim that would usually only be used on race day to precent damage. Open tubulars mount like a standard clincher, but are made in the same artisan handmade process as the tubulars and are not stiff like most clinchers, maintaining most of the ride quality gained from a handmade tubular.
Non-vulcanized: Ultimately the major difference between a handmade tubular or open tubular and the majority of clinchers is that it will avoid the heat and pressure process called vulcanization, which most tires undergo in production. It is used to bind the materials, but compromises the ride quality when the rubber gets tougher and dried out. Challenge tubulars and open tubulars are hand-glued, and the latex and rubber maintain its ideal quality.
It’s the ‘artisan handmade process’ see?