Fire table surface disintegration over winter
did something cause this... is this just a poor quality product?


Yes and yes. I suspect that freeze/thaw cycles caused this damage.


  can I reasonably repair this, and if so how?


It's hard to tell from the picture but it looks like this is a resin/fiberglass material (you can see glass mat fibers in the broken spot at lower left of picture).

You could fix it by removing all chips and dust and applying a resin putty filler (like auto-body filler/Bondo). Resin filler is easy to work with and shape if you have some experience with it.

You will still have an aesthetics issue because it will be ugly; however, you could prime and paint the whole top a color of your choice.

I do not know what you paid for it, only you can assess repair effort versus cost for a new table. I would try to fix it if I were in your shoes, but only because I hate to throw stuff out and I have filler on hand at all times.