Well, the good news is you did not dump $1300 for a rifle worth half that. Any Armalite is worth a grand in just about any market, and today with current events, even if it is not a NM you got an OK Price. I paid more than that for my NM match (M15A4-T) rifle over 15 years ago. The NM does not say anywhere on the rifle that it is a NM. It will say it on the box though IIRC.
I think you have the M15A4 rifle which looks like a standard AR-15 but it will have the bull barrel under the handguards and standard looking sights. But they may well be NM sights if they are of the fine adjustment, 1/4 MOA windage, 1/2 MOA elevation. There is no way to tell by looking so far as I know so read your manual.
Here is a link
to the rifle I think you have and if you got it for $1300 you got it for over a grand under MSRP so you did quite well.
As to the trigger, do you know how a two-stage feels? You said you don't think it is, but if you know two stage triggers there is no think. It is or it isn't and if you are familiar with them there is no question. You should feel a light take up of about a pound or two, then a slight stop where a little more pressure fires the rifle. A single stage trigger may have some creep in it but there is not take up, stop, then more pressure fires. A SS trigger will be just a gradual increase in pressure until it fires. The two stage will have a noticeable stop unless you are hogging the trigger back, then one can miss the stop indicating you are at the second stage. Does your barrel have the free float sleeve under the forend?
Whether or not it is a NM I think you have the NM sights and trigger but even if you don't you did not get screwed at all.