How to confirm how many MongoDb documents got updated during a bulkWrite?

I have the following MongoDB shell script which is using bulkWrite to update a single document.

Here's the catch: it's updating an array field. It works! As in, if I manually check the document before and then after, the item has been removed from the array field.

But a bulkWrite returns a specific result object. And this is -failing- to report that anything got updated. But the document -was- updated!

Is there something specific I need to check to see that this has worked?

MongoDB: v4.2

Document

{
    "_id" : {
        "userId" : <some guid>
    },
    "name" : "han solo",
    "teams" : [
        {
            "isMainTeam": false,
            "team" : {
                "_id" : {
                    "teamId": <some guid>
                },
                "name" : "red team"
            }
        },
        {
            "isMainTeam" : true,
            "team" : {
                "_id" : {
                    "teamId": <some guid>
                },
                "name" : "blue team"
            }
        }
    ]
}

Javascript query

let operations = [];

const updateOperation = {
    updateOne: {
        "filter" : { '_id.userId': user.userId },
        "update" : {
            $pull: {
                'teams' : {
                    'team._id.teamId' : {
                        $in: user.teams
                    }
                }
            }
        }
    }
};

operations.push(updateOperation); // Image this has 10 operations. not just 1.

const result = bulkWrite(operations);

Result from bulkWrite -> aka printjson(result);

{
        "acknowledged" : true,
        "deletedCount" : 0,
        "insertedCount" : 0,
        "matchedCount" : 10,
        "upsertedCount" : 0,
        "insertedIds" : {

        },
        "upsertedIds" : {

        }
}

And I can 100% confirm that the array had 4 items in it, and then 2 items were correctly removed. Leaving 2 items .. for that example user, above.

What am I missing here?

EDIT: I just found another post from today which looks like it describing the exact same thing! REF: Why is modifiedCount missing in Mongo bulkWrite() result?