Thank you ... I imagine that it said one of these:
He paced like a lion.
He was pacing like a lion.
It means to walk back and forth, back and forth, like you see caged animals do. They are in enclosures that are much too small for them, and they are pacing (walking with determination) back and forth from one end of the cage to the other, initially in anger and frustration, looking for a way out.*
*At some point, in the real-world lion, I'm sure that anger and frustration resolve themselves into automatic behavior and the desire to be on the move.
It could have said that Patton "was pacing like a caged lion" or that he "paced like a caged lion," but "was paced like a caged lion" would be terrible English.
The simile is to the behavior of caged cats that get bored in confinement. They walk—pace (verb)—back and forth in their cages, from one side to the other. You can look up "pace" in the WR dictionary. Be sure to look up the verb; "pace" is also a noun.