Sure it's meant as a joke; mentioning powdered milk or bread being from the second world war. Probably obvious that food woudn't have been surplus, but what about equipment? Did the US arm other nations with their older stuff?
Yes.
Most of the US equipment was built for World War Two. It's worth keeping in mind that the average age of a Korean War era M1 Garand would actually be younger than many of the rifles carried in Iraq circa 2003 or so.
In practical terms, most of the equipment used by the US Army if it hadn't been built for World War Two, it was the model largely identical to the World War Two edition. The only major hardware that I can think that was not entirely of that vintage would have been the various jet fighters of the conflict (plus the F-82, but that was a designed for but not arrived in time for war), the M46 tank (which is basically the very late war M26 with improved automotive elements), the later model M20 Bazooka I think was post war (or immediately before end of conflict, etc, etc.)
Basically there were large lots of this stuff sitting around that had never been issued, or had been "gently" used stateside and kept for the post war Army/Marines. A lot of the "war use" stuff, especially ground systems like tanks had been scrapped or given to allies (it was often wore out, or more expensive to ship back than to make a new tank, or just pull a never issued one from storage), but again the lightly used to never used stuff in the US would serve in Korea.
As far as food goes, actually anything that was canned or preserved stood a chance of being World War Two issue, it was less than five years between VJ Day and the Korean War kicking off, well within the shelf life for such things (simply as a modern example, my first MRE circa 2005 had M&M candies with a contest tied into the 1992 Barcelona Olympics, rations and preserved foods are inspected regularly, but they have long shelf lives).
The US gave significant amounts of World War Two equipment to it's Allies. The South Korean Army definitely used extensive WW2 equipment, and many of the other UN countries that did draw US equipment would have had a similar experience (as simply an interesting tangent, while the Canadian Shermans in Korea would simply be US Army ones issued in country, the tanks Canada had back in garrison in North America were actually Sherman tanks...built for the Soviets, and kept when the war ended and then sold of at fire sale prices to the Canadians)
Its worth noting that in Korea in the early 50's the US military was stuck using many pieces of late or immediate post WW2 equipment simply because in many cases nothing new was really bought or funded in the late 40's.
Some new vehicles were developed, some new designs and variants bought, and productions runs completed or cut short. But the budgetary situation in the late 40's wasn't great for the newly combined Dept of Defense. Like after previous wars there was a drive under the Truman administration to heavily scale back the military spending levels and size, it would only be Korea itself and the growing Cold War tensions that would spawn large peacetime establishments in the US by and large.
Nor was what funding was left applied evenly, the newly ascendant Air Force won many early battles, with the promise of nuclear weapons and strategic bombing and jets rendering conventional ground and naval forces redundant and only necessary in support. This paradigm would of course be shown to be sorely mistaken in Korea and directly contributed to the lackluster unprepared state of the US military to respond tot he conflict. So while new models of jet aircraft came online, other arms and branches withered to a degree.
For instance the US Navy commissioned less than 20 new surface combatants or capital ships between the start of 1947 and the end of 1950, with the majority of those being small destroyers at the tail end of the Gearing Class production run. With other projects including the promising early super carrier the USS United States being cut all together.
By 1950 the fleet had shrunk from 30 full size carriers to just 11 globally(the 3 Midway class and 8 of the later Essex hulls), with just 1 in the Western Pacific able to quickly respond to the crisis. This trend was quickly reversed with virtually all of the other Essex class hulls recommissioned and modernized to serve for several decades more in most cases, and new classes were designed and ordered including the first true super carriers of the Forrestal class. https://www.history.navy.mil/research/histories/ship-histories/us-ship-force-levels.html#1945