From the IRC.
- M1502.2 Duct termination. Exhaust ducts shall terminate on the outside of the building. Exhaust duct terminations shall be in accordance with the dryer manufacturer’s installation instructions. Exhaust ducts shall terminate not less than 3 feet (914 mm) in any direction from openings into buildings. Exhaust duct terminations shall be equipped with a backdraft damper. Screens shall not be installed at the duct termination.

When you look at the manufacturer's installation instructions, you will not see 'Type B Gas Vent Cap' listed as one of the options.

Also, this from the IRC.
- SECTION M1302

- - APPROVAL

- - - M1302.1 Listed and labeled.

Appliances regulated by this code shall be listed and labeled for the application in which they are installed and used, unless otherwise approved in accordance with Section R104.11.

Those are listed and labeled as Type B Gas Vent Caps, not 'dryer exhaust' caps.

__________________
Jerry Peck, Construction / Litigation Consultant
Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )