They are different things that are often lumped together with same phrase. Pedal boats called paddle boats and vice versa.

Properly a pedal boat is a boat powered by pedals and a paddle-boat is a boat powered by paddles.

So some pedal boats use paddles or paddle wheels. Others drive pedals to drive a scull. There others that uses pedal driven propellers.

A pedal boat with a hidden paddle wheel.

A hydrofoil pedal boat using a propeller! (image from human-powered-hydrofoils.com - this is not an endorsement!)

Some paddle boats use actual paddles and some use paddle wheels. Some of the vessels using paddle wheels can be quite large.