It is. But...one other thing I thought of based on the description of the scene;
Hands folded on chest, no wrinkling of the bed clothes...
It is also a possibility that Justice Scalia took his own life. Had a fun filled day, retired to his room...ingested something that would present as a heart attack and laid down on his bed and waited.
We'll never know. I'm only saying...based on the description of the scene...it's possible. Unlikely, but possible.
I just asked if he killed himself on another thread not thinking that was the case.
But yeah, he could have had cancer.