Doubt on how dashboard is selecting the index

Thanks Anton it clarified.

Reg the dashboard itself im facing issue when i did management>export [full]dashboard> dashboard.ndjson and im trying to re-upload it using REST API's then im getting 400 error like Child attribute is not accepted or value should be in array. Could you pls help in resolving this issue.

Here is the link for the question asked. Issue with reusing dashboard on another index