What is the difference among these 3 food items: Flattened Rice, Chiwda and Poha?
In India, flattened rice are Poha. Now poha/flattened rice come in packets with the picture you have put. There are a lot of recipes which we make from flattened rice.
Interestingly the most common recipe is known as 'poha'. Here the flattened rice are soaked in water and then they are heated in oil with spices, onion and/or potatoes.
Here is the recipe
This is a very popular recipe in Maharshtra and basically almost all Indians prefer this recipe for breakfast.
Now flattened rice are also used to make chiwda.
This is rather crunchy, unlike poha.
It is used as an in between meals' snack.
Here generally, the flattened rice are roasted or fried.
Now interestingly the varieties of flattened rice for making poha and chiwda are different.
For making poha and fried chiwda  the flattened rice are long narrow type.
And for making roasted chiwda flattened rice is wider.
Hence, to summarise, the term 'poha' is both flattened rice, as well as a recipe made from flattened rice. Chiwda on the other hand is different.
If you go to an Indian restaurant and ask for poha, they will give you a dish made from flattened rice/poha.
On the other hand if you go to a grocery shop and ask for poha they will give you flattened rice.
I hope your doubt is solved.