Definition of confirmation time in blockchain.info What will be the definition of confirmation time and data used for

https://blockchain.info/charts ? 

I would appreciate confirmation.
I believe the data presented on blockchain.info's site is collected by the following method:


a blockchain.info node hears about a new transaction. It is added to the node's mempool, and an entry that includes a timestamp is also recorded into a local database
when the node hears about a new block, it will check to see which transactions are included. It will then compare the time the transaction was first seen, with the time the block was first seen, and the difference between the two would be a 'time until confirmation'. 


This chart reports the median time for transaction confirmation, but note that it excludes any transactions with zero fee. 

It is potentially worth noting that some transactions are published with a low time preference, meaning the person initiating the transaction may intentionally include a low fee that will take a while to confirm, and this would drive the 'average confirmation time' up, even though the network is functioning well for it's users.