Just adding to what WildCard has already stated, 1440p does not equal 2K, I a way, they are both 2 different terms.
2K or 4K is a category of resolution, whereas the 2560x1440 is the resolution itself. and 2K in a sense means roughly that it has at least 2000 pixels horizontally.
So 2K can actually include:
2560 x 1440
2048 x 1080
This is also why sometimes you'll see people refer to 2560 x 1440 as 2.5K because it as 2.5K horizontal pixels.