The page DOES SAY there are two versions of the product...a TB3 version and a USB version.
It does say there are two versions. It does not say there is a TB3 version and a USB version. Look again at the page you linked. [edit: depending on your point of view it either says there are two USB versions - the ones on this page, side by side - or three versions total, a TB3 version and two USB ones]
Maybe they're continually changing the web page, but it looks like there are actually
4 versions all apparently called "Envoy Pro EX":
On the linked page there's a 980MB/s USB-C version (more accurately, a USB-C connector running USB 3.1 gen 2 protocol) alongside a 400MB/s "USB 3" version (more accurately, a USB 3 micro-B connector running USB 3.1 gen 1 which is effectively the same as USB 3.0).
There's also a link saying"Need more speed? Get up to
2800MB/s with Thunderbolt 3!" (i.e. ~28Gbits/s) leading to a page describing two variants (regular and 'video edition') of a full Thunderbolt-3 version.
I'm not sure what "Thunderbolt 3" compatibility really means beyond being able to plug it in without enjoying the full speeds
Obligatory XKCD:
(Or see
TVTropes... for a fuller explanation at the risk of wasting rest of your day)
I.e. It's one of those 100% true statement and 100% misleading statements from the department of redundancy department.
All Thunderbolt 3 ports are USB-C connectors that also support USB 3.1 host* mode so pretty much
any USB device is 'Thunderbolt 3 (port)" compatible - although most wouldn't quite have the brass neck to apply that to a product that only came with a USB A connector.
* the other way around - connecting a
true TB3
peripheral to USB - is more complicated: any dual-protocol USB/TB3 peripheral used to need separate TB3 and USB 3.1 'input' ports, even if they were both USB-C connectors. The latest TB3 controller chips - released - early this year ISTR - potentially allow peripherals with TB3 ports to 'fall back' to USB 3.1 - but
only if their innards can cope with both USB 3.1 and PCIe (from TB) protocols. The true TB3 version of this particular drive doesn't support USB 3.