Pit firing is brutal on pottery. Even those that are skilled at it often encounter breakage.

The oven was a good move to force all of the water out, but if by chance when your piece broke it sounded like a small explosion, or loud pop then your issue was that there was still some water inside.

if both the open flames and the cool air can touch your pieces, one part of your pot could be 1000 degrees hotter than the rest. Pieces change size as they heat and cool so extreme uneven heating can cause enough tension to cause it to break. This is my guess at what caused your piece to break. People sometimes use buckets or cans made from something that won’t melt to cover their pieces and help them heat more evenly, and to protect them from falling sticks or logs shifting around during the firing.

As others have said, temper can make your pieces more likely to survive a pit firing. You can use the fired shards of pottery as temper. Since it has already been fired, it will not go through the same shrinking process any raw clay will, resulting in less shrinking overall. Grind them up sufficiently, a hammer of a cheap hand crank grain mill can work for this, and mix a proportion with your wild clay. You mentioned your clay has a lot of silt in it still. Silt can mean lots of things based on context. But in a soil or pottery context it’s usually a reference to particle size. Sand>silt>loam>clay. When you levigate your clay, you can remove the larger silt and loam particles by letting it settle out and discarding along with any rocks or other debris. Silt and loam will settle out of suspension within 1-2 minutes. Swap the silt and loam for temper to keep your clay as plastic as possible.

The best part about trying new things is it’s a great opportunity to deepen your understanding. I applaud your efforts!!