The Russian reaction can be hardly considered as an overreacting implied to get some political score from EU. Russian reaction would be the same for any other country or untreated decease. It can't be considered as overreacting until the problem is settled down. Probably it is overreacting but we can check it only when the problem disappears.

Actually there is no a big conspiracy theory but sometimes Russian government does care about Russians.

Though Russian government certainly will use the case to get some political score in the second place.