There is no problem here. The speaker has chosen not to backshift, presumably because the speaker believes "he will attend" still to be true, or at least still to be "his" intention.
You would backshift if you doubt if the statement "he will attend" is still true.
Is Joe going to the party?
Yes, he told me that he will attend.
I don't know. He told me that he would attend. But he's not here yet.
There is another alternative. It is possible that with "would" there is no backshifting, and the word "would" was used in its condition sense: "He would come if" or its habitual sense "He said he would go to parties every Saturday while at college".
You need to understand the context to know when "would" is a "future in the past" and when it indicates "conditional"