Why would my valves get smashed?

Timing issues. You would need to dig further to figure out exactly why. Timing chain, guides, etc. Alex

The only thing that could cause valves to impact the pistons is to have the timing be off, such as with a timing chain that is stretched for some reason and jumps the gear. There is no reason to think this should happen, but there's really no other way the valves could get "smashed". I would guess at some kind of other situation where work was performed on the engine, or something gone wrong. It's hard to really know without examining everything in the history of the vehicle. Spontaneous failure can be possible, but incredibly rare.

This article will give you some insight into this matter. 1999 - 2006: https://www.blauparts.com/audi_timing_belt_replacement/30l30v/audi_a4_timing_belt_replacement_kits.html