XQC #84 (Duel)

The engine only records your view when playing.

I thought I had heard/read that the demos recorded the keystrokes of both players - which is how the engine knows how to re-play the games. 

Because it only recorded the keystrokes, it was possible, in the past, to trick the engine to replay the demo on wrong maps. Doing that would result in players running into walls and doing all kinds of silly things.

If the engine did only record the keystrokes, I don't see why it shouldn't be possible to switch views?

The engine only records your view when playing.

I thought I had heard/read that the demos recorded the keystrokes of both players - which is how the engine knows how to re-play the games. 

Because it only recorded the keystrokes, it was possible, in the past, to trick the engine to replay the demo on wrong maps. Doing that would result in players running into walls and doing all kinds of silly things.

If the engine did only record the keystrokes, I don't see why it shouldn't be possible to switch views?

It's not the keystrokes that are recorded, it's the information that the server sends you. As the server only sends players information about enemies that they can actually see (wallhack prevention), you can't switch view in demos.

it was possible, in the past, to trick the engine to replay the demo on wrong maps.

You can still do it by overwriting the map file, but the incorrect map version won't change the information that was recorded on the original map version. So when you view such demo, you'll see the original information overlapping with an irrelevant map with effect such as players or shots going through walls.