So how come if I played the program on my t2 iplayer and after about 15 minutes max I could just save the last streamed content?
p06mvmmris the series PID, as you can see by navigating to it, and isn't supported by yt-dl (yet).
p06mvpswis the episode PID, but (as you note) the high resolution streams are only supposed to be available to certain "Smart" TV iPlayer apps. yt-dl doesn't know how to find these streams (yet). Perhaps no eagles with extremely large disk storage have contributed to the extractor.
The stream URLs are meant for viewing. Quite possibly, they are limited to real-time plus a margin for background buffering.