I don't think there was bad blood with Bram. Rather, vim was always Bram's baby, even with contributions from the community, and he was very opinionated about how things should be implemented. IIRC, he found the new features of neovim interesting enough to want to implement them his own way, and a couple times commented that he thought that neovim's approach to certain features was "wrong," to his way of thinking.
His choices were always a bit idiosyncratic, but the success of vim justified them, so it was never a problem... until he died, and now there are two projects, one of which is very modern, both in terms of the codebase and how the project is managed, and the other is likely to become something of a legacy project unless someone as dedicated as Bram is found to take over.
His choices were always a bit idiosyncratic, but the success of vim justified them, so it was never a problem... until he died, and now there are two projects, one of which is very modern, both in terms of the codebase and how the project is managed, and the other is likely to become something of a legacy project unless someone as dedicated as Bram is found to take over.