Seems certain to me now these are not typos, with missing "a monster appears", I found a new one from Innsmouth involving gypsies at Independence square dancing one open.

IIRC, monsters are only added automatically when a gate opens via Mythos card (or a monster surge). If an encounter card says that a gate opens but does not also say a monster appears, then no, no monsters appear.

Yes true, but my point is when a card says "a gate appears", this isnt a typo, as some people here have thought it might be meant to say "a gate and a monster" instead.