Denys Davydov offers an interesting explanation of the missile strike in Poland.

His suggestion is that Kiev and Lviv were likely cruise missile targets.  If you take the latitude of Kiev and the longitude of Lviv, you get a farm in Przewodow (sounds a little like Zevodov according to Google Translate) which is where the missile struck.

So possibly a marginally intoxicated Russian programmer was looking at a list of different target coordinates, took another swig of vodka to clear his foggy head and vision, entered the blended coordinates, and told his commander, "Она готова!"

Ryan McBeth offered another explanation earlier.  As for the S-300 theory, McBeth mentions that the idea first appeared on Russian social media sites that eventually get picked up by Twitter and others.  In this way, Russian misinformation got traction and circulation and blame fell briefly on Ukraine.

Davydov and McBeth are both great sources, and right now, I think Davydov's suggestion makes the most sense.