Yes - I see the same very small data sets from the 5s running iOS 8.
I also get over-estimates of my step count when running and walking yet somehow over the day, I believe the total counts are reliably the same small over-estimation of my actual effort.
My only conclusion is that the devices need to handle motion data from people with short legs, tall legs, stiff shoe soles, cushioned running soles, pavement and trail runs, etc...
I'm sure the engineers know that some class of people are over counted and another are under counted and my suspicion is that they are attempting to be as close to accurate for as large a group as possible and still work within the constraints on the firmware code size/complexity in the motion coprocessors and not drain the battery more than the allowed power budget for each device.
FWIW - the iPhone 6 is even better at estimating, still has lots of small data bursts logged to health app but still slightly over estimates my effort.
See Edit note at bottom. My answer does need work, but I don't know the correct answer yet.
You need additional accessories to collect that data.
From the IOS8 for iPhone manual Page 122:
Data sources: Enter your own data, Collect data from a device, Collect data from an app.
Also on Apple's "Health" marketing page note it says:
The Health app in iOS 8 lets you see the data that your health and fitness apps collect in one place. You can also store your important health data in Medical ID for easy retrieval in an emergency.
Nowhere in any of the documentation does it indicate that Apple has figured out a way to collect this data with the phones sensors regardless of where the user is keeping/carrying the phone (i.e. shirt pocket, pants pocket, in an arm band carrier...etc).
Apple also sells the accessories in the apple store.
EDIT to add: Now I'm confused too!! today My iPhone 6 has data collected, and I don't know how from the research I've done for this answer. The interface seems incredibly buggy, I am seeing both NO DATA and graphs populated with data and I can't see apparent methods to make either happen intentionally. Drilling down to the "All Data" display and waiting a long time does seem to return data points that the phone has collected.
Additional Info Edit: NO DATA seems to appear while data is being sorted, that's my feeling anyway, I can't seem to figure out what makes sorting short or long however.
I've googled and searched apple additionally and can find no apparent documentation other than what I've already linked and quoted.
Best Answer
This is required for the EasyRide functionality. The first time you activate it within the app you are asked to grant access by iOS.
(EasyRide wants to access your Fitness data to optimally support you, e.g. if you forget to sign-off after a trip)
If you decline you can't use the EasyRide functionality
You can check in System Preferences -> Health whether the SBB app has access to its data or not. Access can also be revoked from there.