No, you are not using MPTCP to connect to this website!
Brought to you by mod_mptcp, a MPTCP module for the Apache Webserver.
MPTCP is a proposed extension to the TCP, allowing to use multiple paths for a connection. This allows for combination of bandwidth available on multiple network interfaces or seamless roaming between different type of access networks.
All you need to do is to access this website with a device that supports MPTCP. C. Paasch, S. Barre et al. implemetend MPTCP in the Linux Kernel and provide a modified Kernel to use on your system. Simply follow the instructions on the project's website to enable MPTCP on your device.