But the port will tell you which generation it is, because USB 3 has logically a separate hierarchy than USB 2; it's just that these two hierarchies get merged on the host side. In fact, lsusb --tree even shows the theoretical connection speed right next to the device, so that's what I'd ask.
It is connected to an xHCI if, and only if, it speaks USB 3.
Other than that being USB 3, this tells you exactly nothing. The fact that your bus is faster means nothing on the speed or quality of storage. You can have good USB2 thumb drives that saturate a USB 2.0 HiSpeed bus at 480 Mb/s (30 to 50 MB/s), and you can have shitty USB3 thumb drives that achieve transfer speeds below 2 MB/s.
Your benchmark shows rates that are far below even USB2 capabilities, so your whole question is moot. You have a very slow storage device, no matter the USB generation. USB is not the bottleneck here.