Here's an important difference.

The 18F post says:

"we reviewed all Google Drive files shared between Slack and Drive, just to be sure nothing was shared that shouldn't have been. Our review indicated no personal health information (PHI), personally identifiable information (PII), trade secrets, or intellectual property was shared."

While the OIG report says:

"[the integration] permitted full access to over 100 GSA Google Drives, resulting in a data breach."