Probably did blow out of the breather tube.

I had the same situation on my X a few years ago....had a flush done at the dealer and it was over-filled. Headed up a steep long grade east of Asheville, NC on I-40 with the truck pulling high RPM's to keep up speed. The guys following behind me came on the radio and told me I was coating their windshield in a film of AT fluid.

Stopped at the first exit I came to and checked my rear hatch....yep it was coated too....as was the undercarriage from the tranny back. Checked the AT fluid level....seemed fine. But I still got on the phone to the nearest Nissan dealer.....

Started to drive over to their location and everything seemed fine. Stopped and check the level again....and the folks following me told me over the radio that nothing was hitting them anymore....So I called the dealer again and told them I would continue the short way on the rest of my trip. Everything was still fine.

Drove it home at the end of the weekend....everything seemed fine. But I took it in to my dealer on Monday morning and they confirmed that the fluid had escaped from the breather and the level was fine. They admitted that they had overfilled the tranny.

That was over two and a half years and approx. 60,000 miles ago.