The correct answer to this question seems to depend on which Greek lexicons and Bible commentaries you consult. In some older Bible commentaries, the Greek phrase συ ειπας is considered assent; e.g.:
1: "thou hast said the truth [and it] is so" (Barnes Notes on the Bible, ca. 1865 A.D.);
2: "'Ye have said,' was a common form of expression for "Yes" (Clarke Commentary on the Bible, ca. 1800 A.D.), and
3: "Thou hast said [was a] common formula, equivalent to 'yes'" (Pulpit Commentary entry at Matt. 26:25, 64).
However, Constable (Expository Notes 2012) writes that "'You said it, not I,' gives the sense of Jesus' response." And I often render συ ειπας as:
a: "You said it, not me", or
b: colloquially as: "You said it, brother!"
Also, Greek lexicons disagree on the root verb in the word ειπας ("said" in KJV). One says it's λέγω and another ἔπω. So, which explanations do you prefer?
Or perhaps he was saying something like:
that might be what you inferred, but it isn't necessarily what has
been said by or implied of me?