That appears to be accurate. BitKeeper froze out kernel developers in April 2005[0] and Git was started the same month[1]:
> Git development began in April 2005, after many developers of the Linux kernel gave up access to BitKeeper, a proprietary source-control management (SCM) system that they had formerly used to maintain the project. The copyright holder of BitKeeper, Larry McVoy, had withdrawn free use of the product after claiming that Andrew Tridgell had created SourcePuller by reverse engineering the BitKeeper protocols.
But as the BitKeeper article makes clear, the relationship between BitKeeper and OSS had been frosty for a while.