They are slightly different.

CloudHealth utilizes the Cost and Usage Report (CUR) that is generated by AWS.  This is the main file artifact that contains all relevant cost and usage information associated to activity within AWS.

Cost Explorer, on the other hand, uses the source dataset that the CUR files are generated from and NOT the CUR directly.

Since the source data is identical, it's expected that the CUR file matches up with that data.  Due to the CUR file begin generated separately from the source data Cost Explorer utilizes, there may be situations where the CUR file is generated incorrectly or differently than the source data that can lead to differences on CloudHealth and Cost Explorer comparisons.