For the upper classes, the common use of metal bowls and chopsticks and spoons dates back to the Goryeo Dynasty, if not earlier. There are older (e.g., Three Kingdoms) metal bowls and plates, but I don't know whether these saw regular use in dining. Upper-class Goryeo diners used porcelain bowls in summer, and metal (usually silver or bronze) in winter. Spoons and chopsticks were usually silver or bronze. Some examples:

• https://commons.wikimedia.org/wiki/File:Bronze_chopsticks_(Goryeo_dynasty).jpg

• https://commons.wikimedia.org/wiki/File:Spoon_of_Injong.jpg (from the tomb of King Injong, d. 1146)

Lower classes used earthenware and wooden dishes, and wooden spoons and chopsticks.

During the Joseon Dynasty, the use of porcelain and metal dishes, and metal spoons and chopsticks was adopted by the middle classes, and by the late Joseon, earthenware dishes and wooden spoons and chopsticks were mostly used by the poorest classes. During Joseon, brass became the most common metal in use for dishes and spoons and chopsticks. Often, one set of silver chopsticks and a spoon would be owned, but everyday-use utensils might still be brass. Upper classes would use silver and bronze. The pattern of porcelain in summer, metal in winter continued.

Traditionally, silver dishes and implements were said to discolour in the presence of poison. This does not appear to have been a common motivation for their use (otherwise, why would royalty - who often had more cause to fear poisoning - use gold rather than silver?). One advantage of silver and brass is that they are bactericidal - bacteria on their surface die quickly. This also doesn't appear to have motivated their use (otherwise, why would porcelain have continued in use in summer?).

One thing that facilitated the use of metal dishes in Korea was the common use of the spoon (in contrast with China, where chopsticks without an accompanying spoon were usual). The spoon allowed the eating of hot soups and stews from metal bowls without requiring the picking up of the bowls (and in traditional Korean table manners, picking up the bowl is very much frowned upon).

In the 1960s, as Korean heavy industry developed, stainless steel rice bowls and other dishes, and stainless steel spoons and chopsticks became common. They were a cheap, robust, easy-to-clean modern version of the traditional metal tableware, and were quickly adopted as standard.

using scissors instead of dining knives.

The traditional upper or middle class meal was served on individual trays, with each dish in its own plate or bowl (similar to traditional Japanese serving). The traditional utensils were spoon and chopsticks. This meant that:

1. There was no need to carve roasts etc., or portion dishes at the table. Thus, carving knives and similar tools were not needed.

2. Food was prepared so that it could be eaten with spoon and chopsticks. Traditionally, there was no need for table knives for diners.

The use of scissors at the table is mostly with Korean BBQ, to portion large pieces of meat (e.g., cutting a strip of ribs into individual ribs). This style of dining, as a common way of eating is very new. Traditional Korean cuisine was very low in meat (i.e., beef, pork, mutton, and other mammals and other mammals and poultry); the main animal protein was from seafood, and many meals were vegetarian. Korean peasants might only eat meat a few times per year. The modern Korean BBQ would have been an unimaginable luxury for most, and the question of how to deal with a strip of ribs at the BBQ table would never have arisen. However, meat-eating has grown in recent decades, with per capita consumption rising from below 5kg per year in 1960 to over 60kg per year today. Part of this has been the growth in popularity of Korean BBQ. Korean BBQ has brought with it the need to cut things at the dining table. Scissors are convenient, since chopsticks can be used in one hand, and the scissors in the other, and items can be cut on the BBQ plate/grill. Scissors don't need a cutting board. Scissors need less skill. Scissors also lack the threatening image of a knife. Since a knife isn't traditional at the table, scissors aren't competing with traditional cutlery for acceptance. With multiple advantages over knives for BBQ use, and traditional not dictating against them, they are a sensible and popular adoption. (Scissors are also widely used in the modern Korean kitchen, so their culinary use will be familiar to many Koreans.)

References:

Growth in Korean meat consumption since 1961: https://i.imgur.com/88YxKPu.png

Hi Soo Shin Hepinstall, Growing Up in a Korean Kitchen: A Cookbook, Ten Speed Press, 2001

Michael J. Pettid, Korean Cuisine: An Illustrated History, Reaktion, 2008.