While the tiles do have in common with aerogel that both are comprised of amorphous silica and air, they are different in many other significant ways. LI-900 is 6% silica by volume, the rest being air; silica aerogel is typically 0.2%–0.5% silica, but has been made with densities as low as 0.1%. LI-900 is opaque; aerogel is transparent. LI-900 can be "plunged into water without damage", even when hot; some silica aerogels will simply collapse if exposed to water, while others have been treated to make them hydrophobic and will probably just break into pieces. Aerogels are usually fairly isotropic, while LI-900 is anisotropic, like felt. Aerogel is made from hydrogel by supercritical boiling — at the time of the STS design, supercritical boiling of ethanol, a process that had resulted in a number of serious industrial accidents, but nowadays of CO₂, while LI-900 is made by dispersing spun glass in water, pressing it into blocks, and sintering.

So it's not the same thing at all, even though it's made from the same raw material.

Seems like they're still very far in density.

LI-900 is 144.2 kg/m³ (9 lb/ft³) and silica aerogel goes around 1,900 g/m3