Some ballpark math: The 1st stage was travelling at 8,300 kph at MECO, and almost of that velocity would have been horizontal. There was no boost-back burn, so it would have kept that velocity until re-entry. Furthermore, it would be re-entering with some vertical velocity. They mentioned that apogee -- when the vertical velocity is zero -- was two minutes prior to the start of the re-entry burn. 2 minutes of freefall would add another 4,200 kph of vertical velocity. So that's 12,500 kph, which is less than 1/2 of a typical orbital re-entry of 26,000 kph. Because the energy grows with the velocity squared, it's more like a quarter of the heat of a typical orbital re-entry.
Finally, as I understand it, much of the point of the re-entry burn is to deflect the re-entry shockwave, effectively creating a shield of "cooler" rocket exhaust around the vehicle.
Still not anything you'd want to take a leisurely stroll in, but nowhere near as stressful as a proper orbital re-entry.
