The spec for this event states that,

When the reason attribute is error, the user agent should set the error message to a human readable description of how the communication channel encountered an error.

But the note in 6.5.2 describes how the user agent should set the message to the beginning of the first failed message. Perhaps we can tweak the note to include both.

See discussion at TPAC

ACTION: @mfoltzgoogle to update close message examples to conform to spec