Nokia 5110 backlight
This just means that the leds on your board (they are not integrated into the lcd itself), have their anodes connected to V+, likely though a resistor. And you control their anodes. Alternatively there is a PNP high side control transistor. 

It's not uncommon to have common anode led setups. Logic is inverted, that's all.

Without knowing the specific board you have we can't confirm. The linked auction provides no schematic or usage info at all, and the LCD blocks the traces on the top side making it hard to trace as well. It doesn't seem to use a transistor. (Assuming you got the exact one pictured. Bay shops sometime substitute similar parts.)

You could unclip the lcd and take good pictures of both sides to see.

A similar version on this blog post shows that it also has an active low light control, connected directly to ground (always on). Another with active low to a gpio. So basically its just a variation on the board layout/schematic. Doesn't really change anything in the end other than the on/off logic.