Tuned in to a dinosaur show on Discovery.
How do they know? For that matter, how do they know it ate 90% of its kill?
They don’t. The vast majority of the the “facts” on those shows that have to do with behavior are simply based on modern analogues. It probably holds true for whatever modern animal they chose to base the Dimetrodon behavior on, but there’s no reaason to think it really applies to this one random prehistoric species. Things about anatomy, environment, and even general diet are usually pretty reliable on these shows, but behavioral stuff should be taken as speculation only.
Also, I’m going to preemptively state, for the record, that Dimetrodon is not a dinosaur (nor, technically, a true reptile)–it’s a synapsid, the lineage from which mammals evolved.
I tuned in a little late. They later said that it was ‘warm-blooded-like’.
I don’t know what “warm-blooded-like” is supposed to mean, and I’m not aware of any bone histology studies on early synapsids, but all the studies I do know of conclude they were probably cold blooded.
“The earliest synapsids were probably ectothermic (their body temperature depended on the environment), as shown by the presence of a large “sail” on the back of edaphosaurids and some sphenacodontids. This sail was composed of greatly elongated neural spines that was grooved anteriorly and posteriorly to accommodate blood vessels, and skin probably connected all the neural spines together. This sail may have allowed these early synapsids to raise their body temperature faster than similarly-sized tetrapods lacking a sail. It was also thought that the sail was used to radiate excess heat into the environment, but recent studies suggest otherwise (Haack, 1986).” (from http://tolweb.org/Synapsida)