Steem is an altcoin created by dan larimer and his team, this coin doesn't have any correlation with bitcoin. I think that you can try to use your search engine to get more information about the history of steem and bitcoin.
Bitcoin is not the same as another altcoin.
Steem can be used to trade for bitcoin with the help of an exchange site that makes it happen.

I think that this is basic knowledge and it seems like you didn't have a lot of knowledge about this. The exchange site is also 3rd party that acts just like a broker.