According to German wikipedia (
https://de.wikipedia.org/wiki/Armenija) the event is described in the KG 26 war diary. I don't have it so can't comment, but the site said the attack was launched by II/KG 26.
I did quick check of the book "Achtung Torpedo loss", the old KG 26 history book, but found nothing about this ship.
The Russian wikipedia also gives interesting details (including WWII Soviet original documents that you may find online).
Both conclude that the sinking is probably not a war crime. Well Germans did commit far enough proven warcrimes in Soviet Union without counting this one.
Edited: I have read that the fact that the ship was sunk by torpedoes or bombs is discussed. The quick sinking is probably due to a torpedo, and the low-level attack described on Russian wikipedis is also probably a torpedo one. Here is what was written in the Kriesgmarine "Kriegstagebuch der Seekriegsleitung 1939 - 1945. - Teil A ; Band 27. November 1941": "Im Kampfeinsatz gegen die Feindtransporte im Schwarzen Meer wurd südl. Jalta ein 8-10 000 t Dpfr. durch LT-Treffer versenkt, südl. Kertsch ein kleinerer Dampfer durch Bimben beschädigt."