It's not a restriction for solar sails. I know that.
But the grandparent comment said "It's mainly targeted at cube sats".
And cubesats tend to be LEO-based. (They tend to be the cheapest thing possible - and its harder to get into a higher orbit. And they tend to be launched parasitically to boot.)
They're hoping to enable cubesats (or at least small sats) to do deep space or planetary missions by proving a low-mass and low-complexity propulsion system.
But the grandparent comment said "It's mainly targeted at cube sats".
And cubesats tend to be LEO-based. (They tend to be the cheapest thing possible - and its harder to get into a higher orbit. And they tend to be launched parasitically to boot.)
Hence, talking about LEO.