A listener who listens via streaming on a web player is the same as a listener who downloads the MP3 to their computer and listens later via Apple Podcasts. Likewise, a listener who downloads an episode to listen to later in an iOS app is the same as a listener who streams that episode in the same iOS app. Listens and downloads are simply unique accesses to an MP3 file.
We do our best to reduce the number of duplicate listens for the same listener, but there are times it becomes tricky. For example, the same listener may listen to part of an episode at home in the morning on their phone, but finish it at work on their computer. These are technically two unique listens even though it's the same listener listening to the same episode. We do however eliminate what are known as 'byte-range' requests. These are essentially requests that skip around to different parts of an MP3 file. Think fast-forwarding and rewinding. So a listener fast-forwarding through an episode will only be counted once.
This said, knowing more about your downloads and listens will be vastly improved as we roll out our new API and Simplecast Analytics 2.0, right around the time Apple will release the new Podcasts app this fall. 👍