I got it working online, but I was logged in and downloaded from Google Play. It just won't work offline for me. I even asked the assistant if it'll work offline, and it told me "I do my thinking in the cloud so I'll be pretty boring offline." She was right. I can't even "call dad" or add to the calendar when in airplane mode. It also didn't work when I allowed it to respond with text instead of a voice.
No idea how random Reddit user managed to do it. Did they say how?