How does Hetzner lie here? They provided unlimited 1-ish GBit/s sustained for every month they were in contract. It is their right to choose to not do business with that user as laid out in the short ToS.
That means a lie was told.
The reason for not continuing the service means they lied. That it doesn't violate their ToS is beside the point—they offered something that they did not intend to let people actually use. The evidence is precisely the fact that they'll stop doing business with you if you actually use what they sold you (and don't agree to pay them more money).
"Well, no, because now we know you'll actually use what we say we provide, and we don't really want to provide what we're offering—that part's a lie."
It'd be different if they'd responded by discontinuing that kind of plan entirely.
This seems pretty straightforward to me.