Looking through the Convective SIGMETs issued that night, at 2355Z, there was a warning of 2 inch hail in an area covering much of Eastern New Mexico. (The SIGMETs are a pain to decipher, so I could be wrong though).

This SIGMET seemed to have deterred most aircraft from flying across that area, but based on flight-tracker PlaneFinder, there were at least 3 other aircraft that flew through that "gap" in the weather. The problem with severe/extreme weather is that it can be localized, so it doesn't surprise me that no other aircraft reported such damage. Based on the track of AA1897 and the weather radar archive, my non-professional opinion is that it flew a little too far north for whatever reason, and went right into the hail core of the storm.

Golf-ball sized hail (1.75-2 inches) at >400mph can definitely cause that kind of damage