Looks like original Docker did Series E in 2017: https://www.crunchbase.com/organization/docker/company_finan...
This is apparently "new/restructured Docker" which did Series A in 2019. From the footnote in the article: https://www.docker.com/press-release/docker-new-direction
It does seem weird to just start the letters over like that, as if it's a new hot startup.