How do you over feed in soil?
The same way you overfeed in any other media: putting too much nutrient ppm into it.
You may be making the mistake of thinking of soil as a purely natural and/or organic media that must, by definition, be healthy for plants. Two problems exist with that thinking.
First, many if not most growers supplement the soil with additional fertilizers. That's pushing up the ppm of nutrients in the soil. If, then, an overzealous grower adds even more nutrients they can raise the ppm above safe levels and thereby overfeed the plants.
Second, even without supplementation the soil can be too rich for certain plants. It's unlikely that natural soil would ever overfeed our plants, but some other plants would die rapidly if transplanted to the average garden supply soil. A good example would be the Venus Fly Trap. Virtually ANY fertilizer at all is too much for a VFT. They've adapted to receive all their nutrition through predatory means, and any food present at the roots will burn them severely.
In most cases with the vast majority of plants you won't find natural soils too rich to grow them. But that does go back to the first point, which is that gardeners usually supplement natural soil with additional fertilizers to improve the growing conditions for their plants. That's where the bulk of overfeeding in soil (or any other medium) comes from: human over-zealousness. The old "if some is good, more is better" mistake.
