I don't even think his agent would tell it like that. First of all Hummels didn't leave on a free and the conflict between him and Tuchel became most obvious when the latter made some snappy comments about Hummels having to be subbed off injured during the cup final. It was again brought up when Bayern hesitated to sign him after they sacked Ancelotti and as far as I remember Hummels himself actually confirmed meeting up with Tuchel to talk things out after that.
There were also reports that he wrote a scathing SMS about his DoF, Zorc, intended for his agent, but accidentally sent it to the man himself.
In his second season he complained to the public that the club bought too many young players (such as Dembele and Guerreiro) and not enough experienced players (such as Toprak, Bellarabi or Schürrle).
This is basically the club's version of Tuchel's handling of the bus attack:
https://onefootball.com/en/news/tho...is-dortmund-players-after-bus-attack-24434868
Schmelzer's (Tuchel's captain) post match comment after actually winning the domestic cup with Tuchel that season:
"I was very shocked by it. I just don't understand it. If a player like Julian Weigl is absent[injured], then the only one who can do it at least on that level, is Nuri Sahin. We all know what kind of qualities he has. The explanation why he didn't play has to be given by the coach. We stand fully behind Nuri.[...]"
Think for yourself how likely it is that someone leaves on bad terms at three out of three jobs, but it's not because of him, it's actually the fault of his three separate sets of bosses. I think he's a terrific tactician and probably a great hire for Chelsea in their current situation, but on a human level he seems to come with an expiration date.