To force BeyondPod to start, the BT device would have to explicitly request BeyondPod, which seems unlikely.

What actually gets started in response to a generic Play command is a bit of a dark art, but it's likely to be the most recently started app. This may be BeyondPod, even if you've shut down the UI, if the most recent action was a BeyondPod background process.

Preventing the device from sending the automatic play command on connection may be the only way to prevent this, I'm afraid.

Another possibility might be to change your BeyondPod settings to reduce the frequency of feed updates.