It is the same conference! They have rebranded this year to Neovim conf [0]. The conference however is not exclusive to Neovim content.
That's confusing to say, at best.
If it's called VimConf, I could understand including content from anything vim related, even vi or neovim stuff (or from the other forks/variations/bases).
But if it's called NeovimConf, I wouldn't expect that to include the entire Vi ecosystem.
According to the FAQs they rebranded because all the traditional vim people complained about too much neovim content.
Apparently the neovim people are more chill about it.
Most VIM stuff works in NeoVIM as well. NeoVIM exclusive stuff doesn’t work as well or at all in VIM.
That will be changing soon. Vim 9 has a new version of Vimscript (called Vim9script) which Neovim doesn't support, and its APIs for things like async jobs are also different. However Vimscript itself will probably remain a common denominator for many years to come.