In my opinion, it would not function as interrogation or alternative explanation.
Here is the sentence.
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か means literally "or" in this instance.
It splits the sentence into the two options you have for turning off the device.
You can turn off the device by choosing from the menu, OR you can long press the button until the light turns off.
Also acceptable in its place would be 「又は」or「もしくは」but the latter seems more formal, so it wouldn't be used in (what I assume to be) a user manual. and 又は I believe is more commonly used at the beginning of the next sentence denoting a second choice that can be taken as opposed to being used in the middle of the same sentence.