The Brazing flow was not drawn out to the lowest part of the joint,
Not unusual for Mass produced Bikes ..
the filler braze wire was probably applied from the crown race seat of the fork crown
while the whole thing was Red-Orange Hot ..

it just may not have flowed fully down to the lowest point,
it seems to have filled to the front and back of the crown-steerer interface.

but it's just a picture.. and remote suppositions.

Strip off the paint, if it looks OK , do a repaint.