Bhagavad Gita, Chapter 4, Verse 5

The Deity said: Many are the births that have been passed by Me and you, O Arjuna. I know them all, whilst you know not, O scorcher of foes.

The real difference isn't how many lives either of them has lived, it's that only one of them actually remembers all of his.

Krishna's answer isn't about denying the timeline, it's about revealing something bigger underneath it. Both have existed across many lifetimes, the real gap is that Arjuna's memory of his is gone, while Krishna's never was.