Yeast as a thickener?

Toast

So I made two batches of cake donuts the other day which contained significant amounts of starch. They were identical in every aspect, except I used 1/2tsp yeast for one and 1/2tsp baking powder for the other. For whatever reason, the baking powder batch was significantly thinner.

My question is, why would such a tiny ingredient make such a world of difference in viscosity? I don't think the yeast provided much leavening (since it was a batter), but it made the dough much thicker. Is there anything I can use in place of yeast to make batter thicker? I've tried xanthan gum, potato starch, and tofu, but they drastically change the texture of the finished product. Is there a difference between active dry and instant yeast in terms of thickening power?

Thanks, you guys are the best.

I suspect a difference in mixing rather than a difference in ingredients.

How closely did the assembly processes match? Time, temperature, mixer, speed, paddle, autolyse?

I don't know why yeast would do that, but I use egg white powder in our breakfast cake.  It thickens the batter and provides rise to the cake without using any baking powder.

1/8 tsp salt
2 tsp Siagon cinnamon
2 tbsp egg white powder (equivalent to 3 egg whites)
1/2 cup oat fiber (about 2 oz)
1/3 cup whole oats milled to flour (about 2 oz)
1 tbsp whole brown flax seed, milled with the oats above
2 cups water
2 tsp vanilla extract
20 drops stevia in glycerol
8 prunes, cut into pieces

Nope, they were both given the same amount of time. I made them side by side to make sure that no factors were off, including temperature, time, etc. I added the eggs and the liquids at the same time. I compared the thickness of the batter at 5 minutes, 15 minutes, and 30 minutes, and the yeast mixture was much thicker all three times.

Baking powder is salty.  Yeast is not.  

Try an experiment:  Take a table spoon of flour place in a small dish, Take a tablespoon of starch and place into another dish.  Give each equal amount of baking powder say 1/4 tsp and add a teaspoon of water.  stir.  What happens?  Now measure another tablespoon of starch for a third bowl, add 1/4 tsp baking powder use milk instead of water.  Any difference?