I've never seen notes like that before so I searched it and find out what it supossed to mean.
Officially there are names for each part of a note:
This specific, (in this case) doubled part is the stem.
I find some sites describing this note type, but first here is an answer directly from here:
Why does this note have a stem pointing up and another pointing down?
Sometimes you'll even have double stems with two different rhythms.
You'll have a half note and a quarter note on the same note. The note
holds for one line and the next line is going on with faster notes
while that note is continuing to hold. There's great complexity and
counter point delineating distinct musical lines. To be able to play
more than one on one instrument, like you do on the piano, on stringed
instruments like violin and cello, and guitar, classical guitar, we
all see these on a regular basis.
I'm glad I find you question because this was really interesting for me as well. I hope I helped :)