Why is the "all downloads" count different than the "downloads" count for some apps?
This discrepancy is actually normal for some free Google Play.
Google provides two different data sets for free apps, the first is a daily number of downloads and the second is a rolling total of downloads up to and including today.
We sum up the daily values to produce the “downloads” number, while the latest rolling total is used as the “all-downloads” number.
Theoretically the sum of the daily values should equal the total, but for many apps this is not the case. Currently, Google does not provide an explanation for the discrepancy between the two data sets, but Google does recommend using the “all-downloads” when looking for an app's overall total downloads.
If you have more specific questions about these two data sets, then we recommend getting in touch with Google directly through the Google Play Developer Console