Maps aside, you will find numerous existing glaciers their today as well as evidence of wide spread coverage.
Pyongyang, October 9 (KCNA) -- Evidences of glacier have recently been discovered around Mt. Kumgang in Korea and scientifically proved. The glacial terrain of the mountain includes a cirque, a u-shaped glacial valley, the site of a glacial lake, a glacial terrace, a heap of moraine, a sharp ridge, a glacier snout, crevasse, moraine, signs of scraping on rocks, curved rocks and holes caused by icy water. Sediments contain many spore and pollen fossils. Most of the spore and pollen fossils belong to the species that are fond of cold weather. Needle-leaf plant pollen fossils were discovered en masse. Fungi and algae fossils were also discovered in large numbers. There remain many descendants of plants that lived in cold weather. The discovery of evidences of glacier around Mt. Kumgang is of great academic significance in that they show there was glacier in a place lower than and south of Mt. Onjin in Yonsan and Suan counties, North Hwanghae Province. The discovery is another scientific and theoretical proof that there was an ice age in Korea.
Sure -- but that doesn't mean that all of Korea was under a sheet of ice.
Also, I think you need to be very careful of this particular news source (North Korean). It would surprise me a lot if this story was not put there for some political purpose.
There was a lot more land there then that is now under water.