Author here.

"Query" does mean "HTTP request" in the summary. It's reported as "Hits" in the stats. Sorry for the incoherent wording ...

The SQL/wpdb support was added afterwards, and it shows because data is only collected but not used/displayed in the histograms.

Phptop is wayyy simpler and not even comparable to SPX, but you can install it in a few sec, use it 5min, uninstall it, and solve lots of common perf problem. That was my use case (it'as ancient code and I barely use it nowadays).