Yes. See my personal opinion and comments below.
I think that your second post above nails the intent here.
During most of my time on the job, our town PD's position was to be extremely lenient on DUI and in fact let folks sleep it off in their cars.
In more recent times, I became aware of the issues discussed in this thread and I vehemently disagree with charging someone not driving but sleeping it off in their car with DUI just because they are in a vehicle and possess keys. I am glad to no longer wear a badge!!!!!
As for the crime of carrying/possessing while under the influence, here's the law verbatim, my comments follow:
The interesting thing here is that if the person does NOT possess a LTC, they can't be charged under this law!!!
Now, to the case that started this thread: If there were no loaded guns in the vehicle, the person is NOT guilty of a 269-10H charge. Some PDs/DAs will still jack a person up on this bogus charge and LOs can confiscate guns/ammo/mags/licenses under "suitability", but no gun crime was committed. However, if they succeed on the DUI charge, the person does get Fed PP status and everything gets confiscated anyway.