..Am I wrong or do dogs bury thing..?

That's not why he reacted the way he did. The prosecutor was frustrated because instead of the botanist conceding the most likely scenario, that the bone was buried under 4 inches of "muck" because it had been there awhile, she comes up with "maybe a dog buried it". And maybe a person buried it, too but neither are likely. It's just one excuse after another by the defense and their witnesses.