"Maybe it's because people saw it as a tool and people become emotionally attached to tools" you may think. Coincidentally his chapter following that is entitled "On Tools" where he goes into psychological literature on human-tool interaction.
---
Also there's an unspoken context here that he gets a step away from a few times without hitting it:
Non-technical people understood computers from their popular depictions; perfect electronic brains; profoundly superior-to-human machines.
Some people likely assumed there was an infallibility to the interaction, as if someone, say unfamiliar with stage magic, saw a magic trick and assumed it was sorcery. People employ whatever mental model they're familiar with that fits best.
The idea it was merely just rearranging your words and feeding it back at you likely seemed just outrageously galling to be the thing a multi-million dollar machine that takes up an entire room and coming from the MIT Artificial Intelligence Lab is doing. No. It must be real...
Almost as outrageous as someone suggesting your sorcerer simply put the item in his pocket while he was distracting you.
Eliza, in 1965 was a computer version of Uri Geller.
---
Another idea relating to Milgram, he never pointed out whether people trusted that a machine would have had safety precautions built in. Of all his variations I'm not familiar with any where he made the machine "malfunction".
Would subjects then trust the proctor but distrust the machine and back off more or perhaps, even more interesting, would there be no difference at all?
― Anaïs Nin
But I take your point that people at the time may have misunderstood the program, possibly believing it was actually sentient. That's a mistake belief, not a delusion.
Go get your hands on a copy, you can probably find one for under $7 on eBay
Pretend someone wrote that program but instead we do a 21st century mechanical turk; an elaborate brain-like device is made with glowing parts, in a glass box, about 8 feet high. There's dozens of wires probing into it and going to these two brushed metal cabinets with noisy fans and blinking lights etc, but it's all just for show.
Inside there's a simple raspberry pi running our program (the turk) and there's a keyboard and monitor hooked up to this theater piece for people to interact.
I would place real money on a very large percentage of people believing it's hard AI, some true breakthrough of science, a heralding of a new age, even though it's just a 40 year old program.
Kinda like how War of the Worlds seems to continually lead to perpetual mass panic when it's just superficially updated and played out as a radio drama - presentation emotes more than content