Memory usage reported in pm2.io does not correspond to what is shown by htop

[scasplte2]

I suspect that the memory calculation displayed on PM2.io may be calculated or labeled incorrectly. In the images below, PM2.io shos that there is 25% memory free with 0.8 GB of memory used (I assume the discrepancy here is just a rounding error). However, when compared to the output of htop when on the machine, I only see ~25% memory utilization.

PM2.io

htop

The number, at least, are in agreement but may be labeled incorrectly on the web portal?
Thanks for such a great tool and service!

[scasplte2]

Now I'm a little more confused, as the number from top seem to be similarly disagreeable

Perhaps, this is because this is a cloud server on shared hardware?

[Kovaelin]

Does pm2-server-monit itself take up significant resources? Has anyone documented how much? Does it increase with the number of processes?