Graves jumped from a 50-52% winrate to 55-56% in every role
... without receiving significant buffs.
The only changes he got were indirect ones, that affected some niche scenarios ( matchups mostly, like the Cait bugfixes or the trundle nerfs ), the Last Whisper change ( that affected equally all the users ) and then lots of buffs that did not affect him but his competitors, making the enemies more powerful.
Still he got this significant change both in jungle and in lane.
What does it mean? Probably the sample size is small, probably during the prior patch the winrate increased during the long month meaning he had a way lower winrate early in the month and a much higher one later ( but still is an absurdly big change), or probably just something else.
What i do want to say is the old tale of "do not post statistical research as a way to support your opinion, use it to make things clearer once those are investigated properly".
was at a what 65% win rate when he was first reworked.