Russians may have an excuse for the initial seizure - a lame excuse, but ...
Russia uses the Cyrillic, not the Roman alphabet. The soldiers that initially seized the Humvees may not have recognized “USMC”. They saw military equipment full of fancy electronic hardware. Russia would see it as an intelligence coup. Now that they have been informed that the vehicles are ours they will be returned - eventually, after being examined.
If the communications equipment was classified it should not have been left unattended.