ambiguous dynamic-ref explanation

[SwimmingPolar]

https://github.com/Automattic/mongoose/blob/master/docs/populate.md#dynamic-ref
Going through this docs, I found the code might be somewhat misleading.

const commentSchema = new Schema({
  body: { type: String, required: true },
  modelId: {
    type: Schema.Types.ObjectId,
    required: true,
    // Instead of a hardcoded model name in `ref`, `refPath` means Mongoose
    // will look at the `onModel` property to find the right model.
    refPath: 'onModel'
  },
  onModel: {
    type: String,
    required: true,
    enum: ['BlogPost', 'Product']
  }
});

...

const commentOnBook = await Comment.create({
  body: 'Great read',
  doc: book._id,
  docModel: 'Product'
});
const commentOnPost = await Comment.create({
  body: 'Very informative',
  doc: post._id,
  docModel: 'BlogPost'
});

I thought properties passed as 'doc' and 'docModel' would be transferred to 'modelId' and 'onModel'.

doc => modelId
docModel => onModel

After some digging maybe it's just typos, please confirm.