The suggestion is that Danchev purposely sent a picture of what is obviously a large transformer hoping or knowing that it would mean something to someone - that the image itself is a message of some sort. I don't think anybody is suggesting that someone "covertly" installed a large transformer in Danchev's quarters to disguise a smaller device nearby.

You're right, it is of course possible that something is getting overanalyzed as we geeks are prone to do, but in the face of what is possibly a bad situation it's worth considering the worst case scenario.