Hi, Docker maintainer here. I'm not aware of any "bad blood", not everything has to be a war or a competition ;)
Vagrant has been super useful to help us get a VM up and running with Docker pre-installed. But when boot2docker came along with a tiny (25MB!) single-purpose VM, 5 second boot time, way less moving parts and no ruby dependency - it just made sense to use that instead. It also helped reduce the confusion between Vagrant and Docker. We had a lot of people who after installing Docker were confused that now they had to learn this other tool called Vagrant, with a complicated ruby syntax etc. Taking Vagrant out of the equation helped with that too.
I agree. There was definitely no bad blood! I was frustrated with dockers stability at one point and made my feelings public. Perhaps I shouldn't have but I also remember saying at the same time that docker is a fantastic idea :) so... not bad blood. Boot2docker has also been great for the ecosystem so it's all good.
Vagrant has been super useful to help us get a VM up and running with Docker pre-installed. But when boot2docker came along with a tiny (25MB!) single-purpose VM, 5 second boot time, way less moving parts and no ruby dependency - it just made sense to use that instead. It also helped reduce the confusion between Vagrant and Docker. We had a lot of people who after installing Docker were confused that now they had to learn this other tool called Vagrant, with a complicated ruby syntax etc. Taking Vagrant out of the equation helped with that too.