Uuuuh, yes you can. You can have an "RNG" that isn't actually random at all. The very nature of a computer (and algorithm) is that it's not random. I haven't looked into RNGs in awhile so I don't know how far they've come, but I doubt that all of them are what we would like to think of as "random."
See: various Fire Emblem games' RNG.
You're simply nitpicking there and ignoring his main point. Sure, the fundamental process of a computer means that random numbers (or other things in general) aren't really random. However, non-random as it may be, it is nigh impossible to trace the generations to a functional and exploitable pattern. By your definition, there is no such thing as a 'good' RNG then, since the generated numbers any machine generates aren't truly random.
The point was that a 'bad' RNG doesn't behave the way it's supposed to behave, i.e failing a 100% success rate objective or passing a 0% success rate objective.