Did anybody see this rock, or take a picture of it, before it blew up? If not, how do we know it was only 1.5 feet across?
Probably not somebody, but something.
The late Louis Frank was hired by the DoD to study the data from a system of satellites that were intended to detect Soviet and Chinese ICBMs. He verified what the DoD suspected -- that the high-altitude flashes were the explosions of chunks of space debris, usually small comets.
It looks like they went through the following steps:
Here's the relevant quote from the ArXiv preprint, Section 3.2 Size Distribution:
"Given the impact speed of the meteor, ∼ 44.8 km s−1, and the total impact energy, 4.6 × 1018 ergs, the meteor mass was approximately 4.6 × 105 g. Assuming bulk density values of 1.7 g/cm3 and 0.9 g/cm3 for Type II and Type IIIa objects respectively, we obtain a radius, R, of 0.4m - 0.5m for a spherical geometry (Ceplecha 1988; Palotai et al. 2018)."This appears to be just an approximation to give an idea of the size, but it's probably about right. I don't think they give an error estimate.
I’m betting some tribesmen has a head hanging inside his hut that he didn’t need to shrink.