Of course it is necessary to burn tokens if their project is not sold out, but we have to ask the team to have specific evidence, if the good team they will tell us all, and if the project is bad they cried but tokens that were not sold out are still there for what purpose, only coughing will know.
They should provide evidence that is accessible to everyone, prior to the token sale, its already indicated that any unsold tokens should be burn so the total supply will be just the total sold tokens which I think the right thing to do. Developers are selling a lot of tokens to cope up the demand in the market but since its not guaranteed that all offered tokens for sell be sold out, that's where the burning of coins happened.