You have your numbers a little bit wrong. The total number of coins is what you are referring to. There will only be 21 million bitcoins and 100 billion dogecoins.
The market cap is their value measured against the US dollar. Bitcoin is at 10 billion at the moment http://coinmarketcap.com/ If dogecoin rose to 100 billion ~10 the size of bitcoin each coin would be worth a dollar.
You are right in that market cap means total value... however, in the context of the article and the comment I was replying to, they meant total coins (where else would the 100 billion number come from?)
Wait... now that I read the above comment again, I think you may be right... they are saying that it would only take the total value (market cap) of dogecoin to be 8 times the current market cap of bitcoins for the dogecoin to be worth at least $1 a coin.
So nevermind, you are right and I was wrong. In my defense, the original comment was a little unclear about what they meant.
The market cap is their value measured against the US dollar. Bitcoin is at 10 billion at the moment http://coinmarketcap.com/ If dogecoin rose to 100 billion ~10 the size of bitcoin each coin would be worth a dollar.