I agree. Actually it could be a very good thing if they used quality
top soil and it's deep, new and just not compacted much. I'd much
rather have that than some hard compacted base. Besides drainage, the
other issues I'd keep an I on is how much it settles relative to other
fixed parts of the landscape, eg sidewalks, driveways, etc. And watch
out for any areas that are noticeably lower/higher than others, as
these things can be fixed easier before the grass gets established.