Are things this shape not called Ikebanas?
Things specifically made for Japanese flower arranging. Low bowls with an opening at one side.
I am not at all sure about whether or not it has been made using the "half-post method" - which is nothing more than a partial casing. The name is old and originates from a process that used to be used in bottle making.
I can see where you're coming from, with the bit that seems to be inside the opening, but I'm not sure it might have got like that when the opening was made. Perhaps a small bubble was blown into it to add a bit of extra metal?