I had a similar experience years ago. I was whizzing along on my road bike doing about 20 mph and I heard the characteristic sound of big knobbly tyres on tarmac coming up quickly behind me. Suddenly a young woman on a MTB went past doing about 30 mph, one hand on the bars and the other holding her bottle. She took a quick drink, called out a cheery 'hi', replaced the bottle in its cage and shot off even faster. I saw her turn off the road up a steep bridleway ahead of me. By the time I'd got to the gate she was almost at the top of a hill way up to my left. Boy, she was fit...
A month later, I spotted her in one of the MTB mags - it was Deb Murrell.
Womens' Cross-country Mountain Bike, Atlanta Olympics, 1996
1, Paola Pezzo, Italy, 1:50:51
2, Alison Sydor, Canada, 1:51:58
3, Susan Demattei, Fairfax, Calif., 1:52:36
4...
22, Deb Murrell, Britain, 2:04:44
...