I'd believe the speed test that was better (only basing on my tests in
the last hour), suppose you'll only really know if you download a big
file where you know you can utilise your full bandwidth.
Try a speed test on a website, rather than the Google Home app. My
Google Home app is reporting I'm only getting ~200Mbps but if I speed
test elsewhere or download a big file, I'm hitting my 500Mbps limit
fine.