Is there a best/correct practice for implementing object-level validation and the ensuing validation errors?

Django REST framework documentation suggests doing object-level validation in Serializer.validate()[1].

To do any other validation that requires access to multiple fields, add a method called .validate() to your Serializer subclass. This method takes a single argument, which is a dictionary of field values. It should raise a serializers.ValidationError if necessary, or just return the validated values.

So if I wanted to evaluate two fields and validate that only one of these fields is given data, I might implement my serializer something like this:

from rest_framework_json_api import serializers
class ProductSerializer(serializers.ModelSerializer):
 def validate(self, data):
 if data.get("best_before_date") and data.get("expiry_date"):
 raise serializers.ValidationError(
 "Specify either a best before date or an expiry date."
 )
 return data

However, using this serializer with django-rest-framework-json-api results in an error response that seems incorrect.

{
 "errors": [
 {
 "detail": "Specify either a best before date or an expiry date.",
 "status": "400",
 "source": {
 "pointer": "/data/attributes/non_field_errors"
 },
 "code": "invalid"
 }
 ]
}

As far as I've understood, JSON:API error objects should have the source.pointer value as "/data/attributes/<attribute>" when an error is caused by a specific attribute, and "/data" in other cases[2].

I thought about raising this as a bug report initially, but I'm not sure if this is actually a bug or if I'm just approaching this issue incorrectly. I also made a complete minimal example with unit tests of how I've implemented this.

[1] https://www.django-rest-framework.org/api-guide/serializers/#object-level-validation
[2] https://jsonapi.org/format/#error-objects