Hello Arpa,
Unfortunately, there is not much information available on Alexandre Atabekian other than what is published on the websites you pasted from, and archives that are not accessable on the internet. I first read about him in an essay entitled "non-western anarchisms," which is very informative and available in full-text on the Anarchist People of Color website [www.illegalvoices.org]. I've never heard of Levon Atabekian, but it's perfectly possible that the two have been confused by historians.
I'm not sure why his last name is of Turkish influence, but I know that Alexandre Atabekian was definitely Armenian
