Are these like flashbacks from before he found out that he was a vampire?

yes, it’s before the start of the story :)

More like prequel or episodes before they became an item or thing or any of this story was started.

yes, if you've read the author's note(epilogue). it says there that the extras would serve as a "prequel" where it takes time before the story started

Yea I never read the epilogue’s