There are so many holes in this story that aren't adding up.
Let me try and just explain, not saying you are wrong. I'm wondering how legit this new dealer you went to is.
I was driving on a highway and suddenly there was no response from the engine (i could feel the car decelerating). Then the engine started responding again
This is not normal for a lack of oil, or oil pressure. Unless it went into limp mode (to protect itself due to lack of oil pressure for more than x minutes). Also you mention nothing about a CEL (check engine light), or low oil light. A low oil light comes on any time the vehicle detects 2 quarts low or more on oil ( this is for all manufactures ). So there is no way you went from no light, to engine stalling without this light ever coming on.
You then say
(oil pressure, abs and a few others)
Again, this sounds like the CSL (check system lighting) function whenever you turn the vehicle on and all the lights illuminate. This is so you know all lights work, at this point it sounds like the the engine was simply died, from who knows what reason. I'd bet recall.
You then say
I checked the oil which was near empty. I walked to a nearby gas station and bought oil and tried filled 2 quarts. Then I noticed that all oil drained right through.
The disptick only registers 2 quarts of oil (again this is across all manufactures). So if you seen any on this dipstick, then your vehicle was not empty on oil, low, sure, but this if you seen any on the stick this is why your low oil pressure light never came on. Because you were never more than 2 quarts low, you are just assuming you were due to lack of knowledge (not making fun).
You then say you seen oil drain out, these are very sensative to adding oil, too fast it runs out of the dipstick tube, or can easily overflow through the top of the filler neck, which is placed under a very cool looking plastic shroud, so you probably never seen oil "coming straight out" you probably simply added to fast and seen it coming out.
Heres where it gets sticky
I had the car towed to a nearby Hyundai dealer. The dealer diagnosis was that there is no drain plug which is probably because the last place the oil was changed (around 2-3 months back) did not install the plug properly.
So YOU never visibly seen the oil drain plug missing before the vehicle went there.
My bet, off your story. Dealership you went to is trying to get a customer pay engine job over a warranty one because it pays twice as good.
-10 years working at a dealership in service.