Podcasting Apps Using Internet Even with Downloaded Episodes

I’ve been using a couple podcast apps, Podbean and Pocket Casts most recently. If I run an internet speed test from a PC on my network, I find that while playing a downloaded episode from my phone there is very little bandwidth remaining for the PC (0.2 MBPS). If I stop the episode or put my phone in airplane mode, the results on the PC are back to normal (40 MBPS).

Is this a feature of Android or simply poor use of resources by the individual podcast applications?

Is there a way, besides putting the phone in airplane mode, to stop the app from using internet bandwidth while playing a downloaded episode?