That’s a claim not a fact. It’s also possible he was an asset for a hostile intelligence service posing as a journalist.
I’m not normally one to side with Mike Pompeo, but I agree with his assessment on this one:
https://www.nytimes.com/2017/04/13/us/politics/mike-pompeo-c...
“‘WikiLeaks walks like a hostile intelligence service and talks like a hostile intelligence service,’ Mr. Pompeo said.”