He's not officially back on STO as yet - and given the current frustration of many of the STO playerbase, might not want too take back the reigns of STO.
That said (assuming this isn't a typo and data error on his Facebook page; I for one would welcome his return to the position of STO EP if he was so inclined (and the suits at PWE/Cryptic were in agreement he should return to the position.)
If he's back I would expect we'd hear something about his return to the company officially from Cryptic soon.
Edited tio add:
Read the redt of the thread after posting the above, them saw this:
Originally Posted by Ashur1
Look into the Celebration thread, he posted there.
Link to the tthread DStahl made a post in using his Cryptic Studios account - so the evidence would seen to indicate he's back at Cryptic - although again, we've yet to hear if he'll be resuming his old position as EP of STO again.