Yoshimura is supposed to be this wise good old man, who was evil in the past. But he has a kakuja and it's mentioned in the Tokyo Ghoul wikia he had to cannibalize to obtain it. If I recall correctly, in the flashbacks when he was an evil ghoul it's never shown he having a kakuja. Did Yoshimura cannibalize after becoming "a good guy"?
This was not specifically discussed nor explained in the manga. But, in Chapter 119,
it was mentioned that when Kuzen heard of the One-Oyed Owl, he took the One-Eyed Owl's place for fear that the organization, V, would find out that the Owl was his child.
Also, if you notice while Yoshimura was telling Kaneki his past, he talks about it in a third-person point-of-view
(by using 'Kuzen' instead of 'I').
While this might be just a style of telling a story, I interpreted it as his dissociation of his current self from his past self. He does not want to be seen as what he was in the past. Furthermore, notice how Yoshimura mentions this in Chapter 119:
'And so, Kuzen took the place of the One-Eyed Owl.' Not 'Yoshimura took the place of the One-Eyed Owl.'
Assuming that Anteiku was established and he assumed the identity Yoshimura afterwards, this means that he cannibalized before becoming Yoshimura. While the wiki mentions that
he was already going by the name Yoshimura when he found out about his child, this was not directly stated nor explained in the manga as far as I know so I have no idea where the wiki gets its information. It was only mentioned that time passed.