Node-centric network metrics are very different from the sum of metrics of the Pods running on that node
I found out what was happening in my graphs. All the Pods mentioned above have one thing in common: they use the host's network namespace, so their network metrics are all identical, and equal to the global host's metric (just with a slightly different precision).
$ kubectl - monitoring get pod -o jsonpath='{.spec.hostNetwork}' \
    prometheus-stack-prometheus-node-exporter-jnhw7

true

$ kubectl -n kube-system get pod -o jsonpath='{.items[*].spec.hostNetwork}' \
    kube-proxy-gke-triggermesh-product-control-plane-7fc0ad24-z586 \
    gke-metrics-agent-5cv4m \
    prometheus-to-sd-tk8jv \
    fluentbit-gke-xh879

true true true true 

One way to see it is to compare the host's metric to one of the above Pods: