That is incorrect. The pistol shown in the picture is an M1911 (not M1911A1). The only "M1911A1 improvement" on it is the arched mainspring housing ("hump-shaped backstrap"). The rest of the gun is pure M1911; including the sights, the short-tang grip safety, the long trigger, the long-spur hammer, the lack of finger-clearance cuts in the frame behind the trigger, and even the diamond-pattern wooden grips.This rare gun was acquired from the family of a man who worked for Remington many years ago. Upon close examination this pistol has all the M1911A1 improvements you'd expect, including the hump-shaped backstrap. And it was made as a new gun, not a modification of a M1911.
http://www.remingtonsociety.com/questions/M1911A1.htm
Now, about the anomalous arched mainspring housing on the pictured gun; it is not mil-spec, given its lack of lanyard loop on the bottom of it. With respect to U.S. military pistols, both M1911 flat mainspring housings and M1911A1 arched mainspring housings had lanyard loops, while commercial versions (such as would be found on e.g. a Colt Government Model [Colt's commercial version of the M1911 and M1911A1]) usually did not.
The gun appears to be a standard M1911 with a commercial (no lanyard loop) arched mainspring housing replacing the correct military (with lanyard loop) flat mainspring housing.
The gun is unusual however, if authentic (by "authentic" I mean, manufactured that way by Remington rather than modified later); in that, as stated in the article, it is completely unmarked aside from the Remington name on the slide. Also, the gun appears to be parkerized in the manner of an M1911A1, or at least, have a matte finish rather than the brushed blue finish of M1911s. If authentic, it would seem that Remington was making a "transitional" pistol (Colt was known to have made "transitional" pistols with elements of both the M1911 and M1911A1 around the time of the changeover). The final 'A1 specs did not happen over night, but rather, somewhat gradually over a period of time in the 1920s.
Remington-UMC of course, never produced any M1911A1s for the military (the typewriter company, Remington Rand, produced enough 'A1s to sink a battleship however). If the pictured pistol is authentic, it shows that they were at least thinking about making A1s.
Does anyone have any more information on this gun?