It was the Stoics and Cicero who concocted and publicized the false report that Epicurus counted pleasure as the greatest good. This is mistakenly asserted in all our handbooks."
You will find that there is a lot of subtlety both in Epicurus and the way DeWitt presents Epicurus, much of which you'll probably appreciate no matter how far you get, and some of which you'll not accept - but having considered it will help you anyway, I would argue.
In this case, I would liken DeWitt's observation to his reference to the multiple meanings of the word "true" in the "all sensations are true" statement.
DeWitt wrote an article on the "Summum Bonum Fallacy" and you'll want to read that part of his book and consider it in detail. I think one way of interpreting what DeWitt and/or Epicurus was saying is that there are mutiple meanings of the word "good" / "greatest good" that have to be considered.
A phrase that I remember from DeWitt is something to the effect that "pleasure and pain have meaning only to the living" and I think that is a very valid point - that Epicurus knew (PD2) that being alive is a precondition even to experiencing pleasure or pain. If that's part of the point, perhaps the issue is that a good can refer to an "asset" (such as for example a house) such that your greatest "good" may be your house (in terms of money value anyway) while it's also understood that in a more basic sense your greatest good is your life or health that allows you to live in it. And there's also "greatest good" in the sense of a "goal" or a "guide."
It does seem clear that Epicurus was wrestling with the Platonists and Peripatetics over straining too much over the meaning of the word "good" as further referenced by that fragment about those who walk around endlessly prattling about the meaning of good.
I sometimes think that it is better to think of pleasure as a "guide" rather than a "good" -- and indeed there's a phrase in Lucretius that Don can help us with the latin on where Lucretius calls Venus / Pleasure what is translated as "divine pleasure, guide of life" (I think it's "Dux vitae, dia voluptas".) Book Two: