Knox is more than in the bootloader, it is built into the phone. It needed the bootloader from 4.3 onwards to work, but it had been there since the phone left the Samsung factory.
Knox is Samsung's secure device within a device for BYOD (Bring Your Own Device) use in the work world. The New bootloader checks whether the device has been "Knox tripped", by installation of a rooted kernel or custom recovery. Doing this trips one bit on a chip from permanently off (0) to permanently on (1) the bootloader reads the bit (in essence it is blown like a fuse - it us what is known as an eFuse) and reports back 0x0 (un tripped device secure) or 0x1 (flag tripped device cannot be guaranteed secure).
Tripping the Knox flag renders Knox (the application useless for ever), but more than that it can be used by Samsung to let them know you have tampered with the software, gained root access and possibly invalidated the device warranty (This is a grey area, you may still get a warranty repair on a Knox tripped device). The "warranty void" next to a 0x1 flag refers to the security warranty Samsung give with Knox.
For ordinary users who have no interest in using a secure device within a device it makes absolutely no difference to how the phone works.
To see your Knox status (0x0 or 0x1) turn off your phone completely and go into download ( sometimes called 'Odin mode') by holding volume down, the home key and lastly the power key down all at the same time. You will get a warning about installing a custom ROM. Ignore it and press volume up. Your Knox flag status is in the small text top left of screen. To go back to a normal. Press and hold the power key until the phone reboots.