It's called "spacetime" because space is inseparable from time. Any distance in space means a distance in time. Things happening "at the same time" are a convenient fiction applicable at short distances. Even things "happening in a particular sequence" is a fiction, if one events is not causing the other: what "happens first" depends on where you are looking from.

Speaking about something beinng N lightyears away from us just means both the distance in space and time. What we are seeing happening there and then is not from our past: it could not affect our past because the light from that event hadn't arrived to us when and where our past was happening, and thus could not affect our local past. We see it happening "before" our past, but observers elsewhere may see it happening "at the same time" or "after" our past, in their frames of reference.