Doesn't detect CVE in Dockerfile FROM imagename

[d3kum1d0r1y4100]

Description:

When the action is used with following config in github actions

       uses: aquasecurity/trivy-action@master
        with:
          scan-type: 'fs'
          format: 'table'
          scan-ref: '.'
          scanners: vuln,config
          exit-code: '1'
          vuln-type: 'os,library'
          severity: 'UNKNOWN,HIGH,CRITICAL'

and a dockerfile containing

FROM alpine:3.11.0

Trivy isn't displaying the cves present in the image name (shouldn't trivy get the imagename from it directly if we are using it in action instead of building from dockerfile and scanning that?)