Why is it called Wired-OR when it is functioning as Wired-NOR?
This is a historic convention.

The preferred active level in many 5V TTL circuits was low as the noise immunity at the input was higher (3V as opposed to 0.8V in the low state). This is the reason we still see pin definitions such as \$ \overline {CS}\$ and \$ \overline {OE}\$ on many parts even though the circuits are not often old TTL; this is simply a convention that has been used for decades.

Noise immunity is the difference between a guaranteed input level recognised as a high or a low (0.8V for a low, 2V for a high in TTL) and the power rail (0V on the low side and 5V on the high side for classic TTL). Therefore the noise immunity of a gate is 0.8V in the low state and 3V in the high state assuming a perfect (5V or 0V) input.

The use of active low is to keep an input in the idle (high state) for as long as possible and only become true for shorter times. That doesn't always work, of course, but the principle is sound.

If we consider an output low to be true (in assertion level notation) and an input level of high to be true, then any true input (high) will yield an output true (low).

From this perspective, it is indeed an OR gate.