The content of the German ultimatum was not a genuine concern, but an outright lie. And it doesn't express a concern that Belgium would ally with France but rather that it would not be able to defend itself.
And I agree with your last statement (except I would have said French instead of Anglo-French, you're having your chronology mixed up again).
This shows how one finds what one seeks. Moltke likely gamed this and if he imagined it then Joffre must be assumed poised to do it. I have in the other thread assumed the ultimatum still flies despite it being after the POD, it certainly draws British fears out but we can debate if it ever goes. When I have Moltke resigned to going East ths ultimatum leaves us and now the British responses must change. The talk is assurances of neutrality certainly, but would Grey not begin to feel out Germany regarding peace and war with France? A shift in emphasis.