Technically he didnt work inside the Trump campaign. He rather infiltrated the campaign via communications with Page, Papadopoulos and another guy. Same principle but through another door instead of actually bring hire
It had to be Comey and/or Clapper via someone else....and HE/SHEs the person we don't know.
This was a "handoff" play. How did it start?
The NYT is trying to sell him as an "insider informant". As you note, he actively infiltrated the campaign and deceptively engaged the campaign staff. He was an active spy.