I've reread the bolded passage several times, and I still read it as "the newly-liberated aruchai reform into what they were prior to being transformed into aruchai".
Are we finished?
Hmm, aren't there some other wall-monsters?
Well, I could also see aberration, but I'm happy enough with ooze here. Huge or Gargantuan (or even Colossal)? Also, I think they've listed sizes incorrectly; a Large creature in 3e has a "10 ft sq" space which is 100 sq ft. I guess they did the same thing here. So when they say 80 sq ft, they probably mean eight 10 ft squares.