Hyundai/KIA has taken older engine designs from Mazda and Mitsubishi (licensed) and has made improvements to them over the years.. They have made some very reliable engines that many do over 300k miles.
Because of the redesigning they call them their own (Hyundai/KIA).
It's a redesigned Mitsubishi engine to Hyundai/KIA specs...
Some of the early Mits engines were known NOT to be very reliable and few got to 100k miles (Dodge Caravan for example).. The changes made by KIA/HYU made these engines VERY durable and they keep on improving upon their designs. So actually them being a "Korean" built engine is very much a positive.
Keep them maintained properly and many have exceeded 300k miles...