the source engine sounds are placeholders for sounds they haven't gotten sound design for, they're replacing these sounds with actual custom ones or just buying the sound libraries for them, most sound effects in stuff like half life 2 are stock sound effects anyways, having sound effects associated with the source engine
not that i have anything against the developer of signal simulator, but that game was not really polished, the gameplay was excruciatingly slow, even by votv's standards (don't get me started on the "power efficiency" system), there were plenty of bugs that lasted months longer than they needed to to get patched, if they even got patched, and the events used in it were just "look at this cool thing happening"