*Interesting. He wonders if this man might be divorced like he is.*
Well, that would be another option, but it's one that's not given to us in the context of the problem. The other thought is, if there was a guard willing to be bribed to skew the scenario one way, this guard clearly doesn't care about the fate of the soldier. So, it's possible he might switch the doors around, tricking the soldier. Or, he could replace the tiger with the rival and still trick the soldier.