Accidental HFWO?

Had the first successful session in over a week, 8 days without ejaculation. The few successful sessions I've ever had have all been dry or dripping pre, but nothing like the most recent session. Ten minutes in, an unbelievable pressure built up and a very surprising gush of watery cum with the regular raw smell came out, followed by a refractory period. I'm wondering what could have triggered the ejac. I had a blanket on since it was a little cold inside, so maybe the slight touch of the blanket? I could have never achieved this with just the touch of the blanket and no prostate stimulation though. Any similar experiences?