Doesn't look like it. iPhone is definitely counting cycling as steps. I just took at 15 mile ride this morning with the phone *in my seat bag* (not on me), which was logged as 15 miles of cycling by Strava and about 3,700 steps by iPhone. I did, however, have Health set to allow Strava to write walking/running, so I turned that off and took a short 1.5 mile test ride, which still logged about 130 steps. Not sure why that should make a difference anyway because I was logging cycling in Strava, not running.
The difference in my 15 mile run and my 1.5 mile test run, if I extrapolated that to 15 miles, would come to about 2,400 steps, so there may have been some improvement by setting the walking/running to off, but not sure why. I'll try again next time I go on a long ride. Regardless, it's definitely sloppiness on either Strava's or Apple's part -- I'm betting iPhone -- but still inexcusable of Apple to log multiple simultaneous activities like that. They should do better, and they certainly know about this issue.