Is GraphQL pushedDate unreliable?

Hi community,
I’m using the GraphQL API for https://github.com/AndreMiras/gitpop3 and realised the pushedAt field may not do what I was initially expecting.
I thought pushedAt returned the date of the last commit or at least the last project activity.
However when I query the pushedAt field for all the django/django forks, something surprising is returned.
Here’s the query:

{
  repository(owner: "django", name: "django") {
    forks(first: 3, orderBy: {field: STARGAZERS, direction: DESC}) {
      nodes {
        nameWithOwner
        stargazerCount
        pushedAt
        object(expression: "master") {
          ... on Commit {
            committedDate
          }
        }
      }
    }
  }
}

Here’s the response:

{
  "data": {
    "repository": {
      "forks": {
        "nodes": [
          {
            "nameWithOwner": "django-nonrel/django",
            "stargazerCount": 215,
            "forkCount": 84,
            "pushedAt": "2020-08-29T14:23:26Z",
            "object": {
              "committedDate": "2013-02-24T17:35:08Z",
              "history": {
                "totalCount": 13990
              }
            }
          },
          {
            "nameWithOwner": "andrewgodwin/django",
            "stargazerCount": 26,
            "forkCount": 2,
            "pushedAt": "2020-04-12T16:14:37Z",
            "object": {
              "committedDate": "2019-04-12T13:15:18Z",
              "history": {
                "totalCount": 26823
              }
            }
          },
          {
            "nameWithOwner": "FlipperPA/django-mssql-backend",
            "stargazerCount": 18,
            "forkCount": 2,
            "pushedAt": "2020-03-14T22:44:44Z",
            "object": {
              "committedDate": "2020-03-13T11:06:28Z",
              "history": {
                "totalCount": 28017
              }
            }
          }
        ]
      }
    }
  }
}

As we can see the top fork (by stargazerCount) is django-nonrel/django and has a "pushedAt": "2020-08-29T14:23:26Z". I’ve checked on the repo cross branches and most recent commit was 6 years ago which doesn’t match with what pushedAt returned. Then I’ve also checked all project activities, by looking most recent issues and PR, but I couldn’t find a date that matched with the pushedAt field.
So my question is what is pushedAt supposed to do? Or could it be that this is the date for a branch that was later deleted without being merged?
Note that for last commit, the committedDate field seems to work OK so far.