Whoppers About Luther from Eric Metaxas

I was driving to a gig today listening to Focus on the Family interview Eric Metaxas who has a best-selling book about Luther and the Reformation. Eric said that before Luther, there was no congregational singing in the Catholic Church:

Eric: "Everything we take for granted in the church today started with Luther. I mean, imagine, he pulls away from the Catholic church. There was no congregational singing. Imagine there’s congregational singing in Catholic churches today, okay. There was no congregational singing. It was just the monks doing the Gregorian chants and so on and so forth. So, if you came to a service, you’re not singing.

Jim: You’re not participating.

Eric: Luther changed everything. He said, the people must sing. Their faith will be deepened by the lyrics of these Psalms and things. We’ve gotta make … we’ve gotta take these beautiful lyrics and we’ve gotta make hymns and we have to have the people sing hymns.

So, Luther very quickly said we’ve gotta invent our own services if we’re breaking away. Well, what will we do? He didn’t want to change too much from the Catholic church. He just wanted to improve these different things.

But one of the things, he made the sermon central and he incorporated congregational singing. So, today any time anybody in the church sings a song, by the way, it started with Martin Luther."

Whoa! I was really taken aback by this considering that Mr. Metaxas is a well-respected author and I would have to assume did good research before writing his book. Why would he say stuff like this? 

Let's look at the facts:

Three hundred years before the Reformation, the pope comissioned Saint Thomas Aquinas to compose a mass for the Feast of Corpus Christi. This included the sung responses (known as propers) as well as three beloved hymns that are still sung today: Tantum Ergo, Pange Lingua and O Salutaris Hostia.

This alone should dispel the myth that Luther began congregational singing. But if not, consider what a Reformed Protestant theologian  Dr. Peter Leithart wrote :

"Beginning in the early thirteenth century there are many references to vernacular songs sung before and after the sermon. The vernacular Christ ist erstanden was interpolated into the Easter sequence Victimae paschali and sung by the entire congregation, this practice being widespread. Other vernacular hymns were later interpolated between the lines of the Christmas and Pentecost sequences as well, and the Lutherans retained what was to them an ancient tradition of singing these sequences with their interpolations on the appropriate days” 

Here's the full article.

Why would Eric Metaxas make such a huge historical error?  I have not read the new book but I question if there aren't other historical inaccuracies placed to put Luther in a more favorable light and make the Catholic Church appear dour and its congregants disengaged from the service (Mass).