Unless their "day job" was law enforcement I'd hazard that they were overstepping their authority. Do you remember if they were officers or enlisted personal? Did you or anyone challenge them on why they were stopping everyone who were riding or walking along a public trail that just happened to pass close to their armory?

How close to the trail is the armory? I wonder if anyone had bothered to tell them that there is a little thing called the Posse Comatose Act that limits the power of the local governments and law enforcement to use in using Federal Military Personnel to enforce the law of the land.

I don't know if this would apply or not, "It does not refer to, and thus does not restrict or apply to, the National Guard under federal authority from acting in a law enforcement capacity within the United States." as it may have just been the Unit's commander feeling understandably nervous but still they may have as I said overstepped their authority.

Did they give you any indication of whose authority they were acting under?