HPA labelSelector not filtering external metrics - kubernetes

Question

I'm trying to setup custom metrics based autoscaler on a EKS cluster (v1.13.10-eks-5ac0f1) but looks like the labelSelector filter for external metrics labels is not filtering.
Using k8s-prometheus-adapter and metrics-server(v0.3.6) I've managed to export metrics from prometheus as kubernetes external metrics.
The metric is correctly exported and visible on the kubernetes api:
kubectl get --raw "/apis/external.metrics.k8s.io/v1beta1/namespaces/*/sqs_queue_messages"
{
"kind": "ExternalMetricValueList",
"apiVersion": "external.metrics.k8s.io/v1beta1",
"metadata": {
"selfLink": "/apis/external.metrics.k8s.io/v1beta1/namespaces/%2A/sqs_queue_messages"
},
"items": [
{
"metricName": "sqs_queue_messages",
"metricLabels": {
"__name__": "sqs_queue_messages",
...
"queue_name": "temp-queue"
},
"timestamp": "2019-11-07T21:14:44Z",
"value": "0"
},
{
"metricName": "sqs_queue_messages",
"metricLabels": {
"__name__": "sqs_queue_messages",
...
"queue_name": "random-queue"
},
"timestamp": "2019-11-07T21:14:44Z",
"value": "0"
}
]
}
horizontal-pod-autoscaler.yml
apiVersion: autoscaling/v2beta1
kind: HorizontalPodAutoscaler
metadata:
name: api
namespace: api
spec:
scaleTargetRef:
apiVersion: apps/v1
kind: Deployment
name: api
minReplicas: 2
maxReplicas: 5
metrics:
- external:
metricName: sqs_queue_messages
metricSelector:
matchLabels:
queue_name: temp-queue
targetAverageValue: "100"
type: External
The problem is that the HPA is not selecting just the metric with the matched label, infact by looking at the logs I can see that the following call is performed
kubectl get --raw "/apis/external.metrics.k8s.io/v1beta1/namespaces/*/sqs_queue_messages?labelSelector=queue_name%3Dtemp-queue"
The expected result is just 1 item (the one matching queue_name: temp-queue label) but instead the filter is ignored and all the results are returned.