I don’t think it was overestimating, more just not realizing that the term “blood libel” isn’t a widely recognized antisemitic concept

Yes...

I overestimated people by thinking if I explained what "blood libel" is, I didnt have to literally say "blood libel is___"

They’re implying the original tweet means threat to kids isn’t from the genocide, and instead it’s the bigoted (and false) stereotype that there are secret Jewish rituals that kill children as blood sacrifices.

When I said "bigoted (and false) stereotype..." You could substitute that for "blood libel". I just pre-emptively explained it not everyone knew what it was.

And rather than ask questions, a bunch of confused people furrowed their brow and down voted.

But you asked questions, so now you know:

Blood libels often claim that Jews require human blood for the baking of matzos, an unleavened flatbread which is eaten during Passover. Earlier versions of the blood libel accused Jews of ritually re-enacting the crucifixion.[10] The accusations often assert that the blood of Christian children is especially coveted, and historically, blood libel claims have been made in order to account for the otherwise unexplained deaths of children.

https://en.wikipedia.org/wiki/Blood_libel