They may have firmed the soil down but left quite a deep tilth for sowing into.
The 'loose' effect could have been made worse by recent frosts which expand the soil surface and effectively fluff it up. That is one of the reasons farmers roll their grass fields in the spring, to firm it back down.

Once the ground is reasonably dry I would give it a couple of light rolls to firm the top a little. The establishing grass roots will also help to bare more weight in time.
If you roll or tread down wet ground you run the risk of sealing the surface.
Air can't get in or out, water will sit on the surface and you will possibly end up with very yellow grass and worse still, moss. Timing is everything.