Orphan Block:It's a valid block that's left out of the main chain because of a temporary issue when multiple blocks are created at the same time.
Key Point: It's a good block, but it doesn't make it into the main chain immediately.
Stale Block:It's a block that was once valid but becomes outdated and irrelevant because another chain in the network becomes longer.
Key Point: It was good before but got replaced by a longer chain.
orphan blocks don't initially make it into the main chain, while stale blocks become outdated due to a longer chain taking precedence.
Also, according to the image above, why is the orphan block still added to the blockchain though is not on main chain of the blockchain?
orphan blocks are good blocks made at the same time, but they don't join the main chain right away. They're added to the blockchain but might be replaced out later for a longer, more accepted chain.