You didn't apparently comprehend what he said. He said "building" not "detonating".
BUILDING a U235 bomb DOES NOT involve any fission except the decays normal to uranium. It involves separating isotopes of uranium, either via centrifuge or gas diffusion to concentrate U235 isotope, and non-nuclear work to set up explosives, electronics, and other bomb detonation hardware.
When you BLOW UP the U235 bomb, THAT is when you get lots of fissions.
The poster you were responding to was EXACTLY CORRECT except for the VERY minor omission of the fact that U235 is going to have some natural decay fission going on, which would be almost indistinguishable from background.
Therefore, he was EXACTLY CORRECT in claming that a neutrino detector would have a VERY hard time detecting manufacture of a U235 bomb.
Congratulations on not only being completely wrong, but arrogant and profane on top of it.