There is consent, but there is also recklessness, and in this case the top was reckless. You NEVER leave someone alone in a bondage situation! It is easy enough to create a situation where there is the illusion that a person is isolated (blindfold, hood, earplugs), but someone should be there all the time. It's hard to ignore that basic safety rules were set aside. I don't know if any other "substances" were involved, but i wouldn't be too surprised if they were.
SMBD play is rather murky when it comes to the law. In MA, as long as it's private and consensual, it's okay. But the problem can be the "consensual" part. If I'm gagged and tied down, how can i tell someone to stop? Is it rape even though I consented at the beginning, then allowed myself to be put in a situation where I have no input, but at some point wanted it to stop?
The mantra for responsible SMBD play has been "safe, sane & consensual". That means each person respecting each other, and establishing verbal and nonverbal signals to avoid dangerous situations.