According to the blog post this site runs in AWS us-west-1. With Fauna you don't know the data center but according to their status page they have infrastructure in AWS us-west-2. Latency from us-west-1 to us-west-2 is 25ms so you can subtract that from the total time.
Fauna claims to route your request to the nearest data center so I'm interested in validating this. Seeing 400ms latency where I'd expect <50ms is important to me, especially on Lambda where you are billed waiting for the response.
Which should be the case, depending on what you do you will probably experience 10-50ms read latencies. Look for Evan's answers why the measured values here are higher.
Curious what Firebase latency would be in comparison, when called from the same GCP data center or AWS.