Github PR triggers push workflows unexpectedly

Question

I have a a build workflow and a deploy workflow.

name: Deploy Staging API & Web

on:
  push:
    branches:
      - master

name: Build Api

on:
  pull_request:
    branches:
      - master
      - release

When I create a pull request from release-10-19 into release, it triggers the Deploy Staging API & Web workflow with the trigger push!

How is it possible that there is a push event that triggers the Deploy Staging API & Web when the PR is from release-10-19 -> release?

As an outcome, I would like the Deploy Staging API & Web workflow to only run on pushes to the master branch, as I think I have it configured.