https://www.speedtest.net/insights/blog/how-ookla-ensures-accurate-reliable-data-2021/
"Multi-server testing
Ookla’s test methodology aims to be the most accurate measure of a user’s real-world network performance. To that end, we have fully enabled multi-server testing on our web, desktop and mobile Speedtest platforms. Testing simultaneously to multiple servers removes the dependency on a single server to fully saturate a connection and measure a user’s maximum download throughput capacity.
Multi-server testing is important because ultra-high-speed connectivity services (such as fiber or 5G) require higher-capacity servers in order to generate enough traffic to saturate an end-user's connection. Peering relationships or cross-connectivity between providers can also be a bottleneck for internet speeds, so a single server’s performance and the proximity of the selected server are both factors that can impact the accuracy of a network test. To mitigate these issues, our applications can now test to multiple servers in parallel to generate sufficient traffic to saturate the end-user's connection.
When a user initiates a test with Speedtest, it opens connections to the four servers with the lowest latency at the start of the download stage. Speedtest dynamically scales the number of connections to each server to saturate the client-side network. For multi-server testing, this connection scaling was modified to ensure that each server in a multi-server test receives just as many connections as it would in a test to a single server. The algorithm for calculating download speed is the same as in our single-server test methodology, except that it incorporates all information transferred across all connections and all servers. All other aspects of the download stage (such as test duration and stable stop) are identical between single and multi-server tests."
You thought that a connection just meant the method of which you access internet like wifi or ethernet, so when you saw multi-connection you assumed it meant LTE + wifi.