The data is collected through Argus app. Playstore install count is "500k+" with 4k reviews, while iOS reviews are over 24k (Appstore don't release download number publicly). Now think about the demographics of iOS users in Indonesia who are health-conscious enough to install such app. Would it be more likely that they ride to their gym or swim each morning and bike in the weekend? How much of those average commuters relying on public transport are going to install such app (which sip non-negligible battery life)?
The researcher compared their data against WHO's 2010 self-reported "percent of sufficiently active", and we're an outlier. The smartphone number of step is in the ballpark of Malaysia, yet the WHO data is similar to Germany & Australia. Other outlier is Brazil, India & Philippines (ok, not as bad as us, but still)