Nucs are often made up with foundation - the plan being that over time (before the nuc is delivered to the customer) the bees will have drawn out the frame and if the queen is any good that fame should be full of brood. Sounds like you got a nuc that didn't have adequate time to grow. This is an often occurrence when people treat getting their bees as the purchase of a manufactured item rather than an agricultural product. That mindset affects sellers too.
Nuc buyers want them asap - ideally with no foundation, empty comb, or drone brood. Lots of brood (in all stages), bees, and just enough stores - not too much, that would be buying honey instead of bees. Oh, and an actively laying queen - not just a bunch of parts assembled right before sale day. And of course not quite swarmy. Not apologizing for any ones weak nucs, but pick a day a few weeks in the future, and try to have a dozon or so fantasy nucs like this ready and just right on your big day.
It all sounds good in theory to say "I will sell no nuc before it's time." But everyone should just try it a time or two.
The 8 frame mediums that I am selling are strong but may have one side of foundation showing on the outside frames today - by Saturday (the projected pickup day) that may be drawn out and they might be starting to get too strong, but if I would let them the customers would have picked them up a week ago - when they would have looked a lot weaker. So what is the best thing to do?