The orbital velocity and the ground track velocity only differ by about 6.6% for their 450km orbit, so it's not a big difference. But because they have a relatively circular orbit, you can use the formula sqrt(G*M/R) which gives 7.639km/sec -- so it looks like they are referring to true orbital velocity.

This is helpful, thanks!

Not an expert. But there are a few ways to look at this.

Bodies that are in stable orbit can have only a specific velocity which is a function of its distance from & mass of whatever it is orbiting. So orbiting satellite's speed can be inferred from its orbital height.

There are ground based tracking stations that can technically measure the speed of any orbiting body.

Also read somewhere that LEO satellites could use GPS receivers to get a fix on their position. measuring change in this position also gives velocity. There a bunch of limiting conditions around max-height and velocity for this to work though.

Ah! Got it. Thanks!

They can measure it by altitude. An orbiting object always has a defined velocity at any point of its orbit. For example, a circular orbit 500km above Earth's surface amounts to velocity of 7.61 km/s everywhere on it.

Makes sense. This is helpful. Thanks, TeMPOral!