Neither of these comments answers the question of how did it survive re-entry, which we have all been taught to imagine as the rocket being immersed in a fireball at horrific temperatures.
The particularly high-heat re-entries of manned capsules, the Space Shuttle, and so forth are unpowered; the atmosphere slows the spacecraft down. The Falcon 9 first stage re-entries are powered; three engines light to slow it down. The physics of how this works are complex and a bit counterintuitive, but the upshot is a thermal environment which isn't as brutal as an unpowered re-entry.
Beyond that, the glass in front of that camera's probably formulated to take extreme heat.
And of course, as jdblair points out, it's starting at a slower speed to begin with; faster than just about any aircraft (except maybe the X-15), but well short of orbital velocity.
Its not just re-entry that makes heat, its re-entry at high speed. The first stage wasn't in orbit. I don't think it had reached orbital velocity and it turned around and fired its engines to reduce its speed even further.
Re-entry from orbit wouldn't just destroy the camera, it would burn up much of the craft as there is no heat shield.
Beyond that, the glass in front of that camera's probably formulated to take extreme heat.
And of course, as jdblair points out, it's starting at a slower speed to begin with; faster than just about any aircraft (except maybe the X-15), but well short of orbital velocity.