On the contrary: if he accepts, he would be, by definition, presumptuously seeking the office.
Bending the definition and nit-picking doesn't make it any more right.
To paraphrase what we all said about Her Crustiness when she ran, "He has never lived there. He doesn't know the people there. He doesn't have an understanding of statewide politics. He doesn't know about the divide between Chicago and downstate. He doesn't understand 'The Chicago Way'."
Now who's being presumptuous?
And no, it is not nitpicking to use the actual words of the definition to demonstrate that it does not apply. If he accepts the responsibility, it will not be presumptuously seeking, but [hopefully/humbly/reluctantly] accepting what the state GOP has explicitly stated is their will. Also, he must be considering at this time whether or not the other alternatives are acceptable.