This king is a smart king, most of you may not notice, but he did a great political maneuver by honoring the dead idiot with the second prize and our MC with the first prize.
The idiot had been a millstone with his hard-headed refusal for "unholy" help and his suicidal tactics, not to mention dying unceremoniously in a flash, so him and any group related to him would have been publically shamed the moment the truth of the matter showed up, so the king decided to "honour" him with a rather high prize in order to cover up the incident and gain political clout (aka. a "favour") over the groups the guy most likely represented, which most likely must've been the conservative nobles, the fundamentalist side of the church and/or a considerable size of the army/knights. And then, by honouring the MC with the biggest prize, one that was one size greater than the dead guy, he pretty much showed everybody that not only did he make an enormous contribution to the effort, but that he contributed more than the other guy, technically placing him higher than the dumbass' associates on the honour spectrum and the king's favour; and to top it all off, the aforementioned groups cannot do anything to him, since attempting any kind of maneuver out of spite or religious belief would jeopardize their own positions, since it would most likely reveal the whole incident with the second place fraud, bringing them far more shame and risking their positions, not to mention it would also make them enemies of the king, to whom they owe a favour for saving their hides. So yeah, they can only smile and wave at our MC without being able to do anything about it ever again, since the king simply finessed them with a simple fraudulent prize.
Now let's just hope the author also realized this fact too and not have everything go back to zero, cause honestly it's tremendously hard to find mangas that know how to do politics and court drama properly.