Molecular nitrogen is inert. So, it may prevent unnecessary chemical
reaction inside the tires. However, its pressure and temperature can be
easily changed. I don't see any benefit of using nitrogen in the tires.

The nitrogen is not a factory installed product, so it was probably
installed by the dealer or a tire shop.

Nitrogen is used in applications where tire temperature control is important
like in some aircraft and race tires.

Nitrogen offers several theoretical advantages but on a practical level, its
benefits are going to be difficult to measure.  The disadvantages to using
nitrogen are the added cost of installing it and the lack of nitrogen
filling stations.

For a car, there is no advantage in filling the tires with nitrogen.
Here are the differences...
1. When you fill with nitrogen, it has been liquified and hence is dry
-- when you fill from a garage air pump, it it is merely normal air
that has been compressed.  So there will be less water vapor in the
nitrogen, but that is inconsequential in auto tires.  In aircraft,
there is a MUCH greater temperature variation, and eliminating
condensation is a benefit there -- you don't want ice to imbalance the
tire when it spins up on landing.

2. Nitrogen will leak a little more slowly through the tire sidewalls,
but the difference is again negligible for automotive applications.

3. The other reason it is used in aircraft tires is that it is inert,
and will not react with the tires.  Aircraft tires get much hotter
than car tires, and they will last longer with nitrogen than air. They
are also much more expensive realtive to the cost of nitrogen, so the
economics makes sense there, but not for a car.