Are you sure it is Walnut and not stained Oak. Walnut rare, it is
difficult to sand , a corse grit will make it black, I dont know why.
For parquet a floor scrubber -buffer with sanding pads is best as cross
grain sanding will be noticable and only more of a fine grit. Parquet
take a pro to refinish it may or may not even be worth it. Some Parquet
is worth a recoat but some cheaper has a wax type factory finish that
new finishes will peel. Tennants may have waxed it or used any number of
synthetic products that will ruin future adhesion of a finish. Id get a
pro for a bid and a look see, It could be as simple as a light sand and
clean, recoat. That minwax says exterior. Exterior products are common
to be softer to allow for expansion-contraction and don`t wear as well
as interior products. Minwax has both. Talk to Minwax, im sure there is
an 800#. Is color even and not worn away, is there a real finish on
it, then it may be worth recoating as also it is a rental not your home.