Tokarev- definitely.
Polish or Russian: who knows. Supposedly Russia still has a lot of Tokarevs floating around.
Keep in mind that Poland added the safety to comply with export requirements to the USA. From my understanding, a Polish Tokarev bought in Poland would look like a Russian Tokarev- no safety.
Poland is closer to Austria than Russia, so it may be more accessible. However, Russian weapons could have been floating around in the illegal gun market, or from the middle east, and obtained by ISIL before sending them to Austria.
my instinct would be to say 'russian', for some reason: more weapons floating around in middle east also for ISIL to latch on to.
However, not enough evidence to prove anything.
From the grip, I thought it might be a ZASTAVA 57, but the slide isn't Zastava 57 type. Plus that would be the same country that provided his assault rifle.
Or, a mix-master? After all, the barrel is the tracked item over there.