The Cisco Meraki throughput test is from the Cisco Meraki device to the Meraki test server. This will will go via your ISP, their transit links, and finally to Meraki. You can consider it a measure of the quality of the bandwidth you are getting. Their is also no guarantee that the Meraki test servers can sustain any particular level of throughput.
On the other hand, if you are connected via a reasonably large ISP, then more than likely the local "speedtest" node will actually be inside of the ISP network, so you are only measuring the performance of your link to your ISP and no further.