Yes they were guilty, no normally that would not result in a sanction of this kind, they'd be fined and life would most likely go on the way it it did before.
Is it entirely a coincidence? Who knows. The Obama DOJ saw fit to fine ZTE 1.2 billion as part of the plea deal. So the conduct was serious. That makes it hard to argue that the punishment for violating the plea deal is some new thing Trump concocted to fuel a trade war.
this presupposes that punishments fit crimes for corporations in our country, and that there isn't rampant partiality
See the separate events in the last decade or so with major players getting minuscule punishments: Goldman Sachs et al, BOA, HSBC, Wells Fargo, etc etc
Maybe they'll decide not to pay and withdraw from the US completely, but that would seriously complicate any future re-entry once the current sourcing bans expire.
My guess is that they will switch to Chinese components and basically become a captive hardware manufacturer for the PRC government, which presumably won't let them fail completely even if their handsets are no longer market-competitive.
extracting a fine from a big foreign corporation is more like a good deal. Limiting the business of your country businesses - hardly so.
AFAIK: We don't know if they violated the plea deal; there is no due process; we only have the claims of an administration that is widely believed to lie. We can't distinguish a political decision from a legal one. (Please correct me if I'm wrong about the process.)
And it doesn't matter what the facts are, it's perception that counts. The appearance is that the current U.S. administration disregards process, fairness, honesty, and the rule of law; is an unreliable international partner; and particularly targets China. The ZTE penalty will be perceived in that context. Any leader must account for perception, whether they like it or not; I think we can fairly assume that the administration is aware of the essential nature of perception, is aware of the perception of this action, and has chosen it.