we have [written] to you so that you may study (carefully) the book of Moses and the books of the Prophets and (the writings of) David [and the]  [events of] ages past. (p. 59)This is section C of the composite text, lines 10-11.
Some scholars have taken the reference to "the book of Moses and the books of the Prophets and (the writings of) David" as a reference to the Law, Prophets, and Writings that make up the three sections of the Hebrew Bible today. Indeed, the note in DJD 10 (© Elisha Qimron) takes it this way:
In this context דויד [David] probably refers not only to the Psalms of David, but rather to the Hagiographa. This is a significant piece of evidence for the history of the tripartite division of the Canon (see § 18.104.22.168). (p. 59 n. 10)This statement goes way beyond the evidence. It is not impossible that a tripartite division of the Hebrew Bible pre-dated the rabbinic era, but we do not have certain evidence of it. The Prologue to Sirach, Luke 24:44, Philo (On the Contemplative Life 25), and Josephus (Against Apion 1.37-41) all refer to multiple divisions of scripture, but none of them refer to the Law, Prophets, and Writings as such. This is old news, though the ideas continue to be debated.
What I want to point out here, though, is that the statement from DJD 10 (© Elisha Qimron) about the tripartite division of the Bible is not from "the editors of 4QMMT," as it is often cited, but is from just one of the editors, Elisha Qimron. Qimron's brief preface clarifies both (a) that he and Strugnell disagreed on some matters of interpretation relating to MMT and (b) which sections of the official edition should be attributed to which editor.
Strugnell has added an appendix containing other possible interpretations of various points concerning which his opinion differed from that presented in this volume. I have also added a short appendix which discusses some points of disagreement concerning the text. The historical discussion (chap. 4) was composed by both Strugnell and myself. The finishing touches were, however, Strugnell's responsibility alone. This explains the disagreement which exists between this chapter and other chapters prepared exclusively by me. (p. ix)Qimron goes on to say that the "major discrepancy involves the problem of establishing the identity of the Zadokites and their halakha," but we may also see some disagreement among the editors regarding the applicability of MMT C 10 to the discussion of the tripartite canon. The note cited earlier gives the parenthetical cross reference "see § 22.214.171.124." This section comes within ch. 4, a chapter on which Strugnell put "the finishing touches," as Qimron tells us in the preface. There we find this statement:
It is not clear whether 'David' refers just to the Psalter, or denotes a Ketubim [Writings] collection, either one that was open-ended, or one that was closed. (p. 112)This is clearly a much more cautious statement than the one we find in the note on p. 59, and this greater caution should be attributed to Strugnell, who was apparently (and rightly) uncomfortable claiming 4QMMT in support of a tripartite canon on the order of the "Law, Prophets, and Writings" known in rabbinic literature and the Jewish Bible today. Strugnell did see MMT C 10 as a reference to a tripartite division of scripture, indeed, perhaps "the earliest tripartite list" (p. 112), and he seems to think that the mention of "prophets" in C 10 must refer to the rabbinic scriptural division called "Prophets," two points that I would want to question. But at least he does refrain from asserting that "David" = "Hagiographa," as Qimron had done on p. 59.
By the way, many scholars have questioned or rejected the idea that we should see a tripartite Hebrew Bible at 4QMMT C 10, and some have suggested different reconstructions of the fragmentary Hebrew text in this passage. Three important articles rejecting Qimron's interpretation are the following:
Jonathan G. Campbell, “4QMMTd and the Tripartite Canon,” Journal of Jewish Studies 51 (2000): 181–90.
Timothy H. Lim, “The Alleged Reference to the Tripartite Division of the Hebrew Bible,” Revue de Qumran 20 (2001): 23–37.
Eugene Ulrich, “The Non-attestation of a Tripartite Canon in 4QMMT,” Catholic Biblical Quarterly 65 (2003): 202–214.