[gruez]

You don't "have to", but they can deport you and refuse entry in the future in retaliation. It's a variant of the TSA not being able to "compel" you to a search, but they can refuse you from flying.

[DANmode]

They can lie, and pretend you’re uncooperative,

or that their investigation took longer than the duration until your intended flight,

but, no, they can’t legally refuse you from flying without cause or suspicion.

[two_handfuls]

The question was: "Does that apply to non-citizens?"

Saying "they can deport you" without specifying whether the hypothetical "you" is a citizen or not means you did not answer the question.

Not that you have to answer a stranger's question, but I thought I would clear the confusion in the hope it may be helpful.

[gruez]

The premise (non-citizen) is in the question and doesn't need to be repeated. C'mon, this isn't grade school where you have to answer questions by first restating the question in its entirety.

[dylan604]

No, but even in grade school, the teacher would get the student to actually answer the question when it is clearly being evaded. Or maybe put the student's name on the board for wasting everyone's time for being obstinate.

[TylerE]

Seems to me you're the one being evasive here.

[dylan604]

How am I being evasive when I'm the one that asked the question? Gawd, how I love the interwebs