My first thought was that it was a small volcanic eruption. But given the fact that people did see a fireball and a large expolsion, and there mass been no follow up activity, plus the supposed chondritic fragments, then it may be a small imact. There certainly is a raised rim.

Some metorites, especially the carbaonceous ones, contain minerals that are reactive in water, that might explain the smell. Also if the grounfwater was rich indissolved H2S you could get some noxious gasses too.

Remember we have neve been up close with an impact this size before so soon after it happened. It took days if not weeks to get to the Sikote Alin site.

It's very interesting whatever it is.