You think Russian intelligence just let him have asylum (and be granted citizenship) without finding everything he knows about how the NSA operates? That'd be extremely naive to believe. Witting, willing, or not, Snowden has been extremely useful to Russia.
According to what I am reading on Wikipedia about the specific timeline, the US revoked his passport before he left Hong Kong. He claims he was planning to fly to Ecuador and was just going to pass through Moscow. And yet there are direct flights from Hong Kong to Ecuador.
The US government is responsible for its track record of completely failing to provide constitutional rights as part of its justice system to people in snowdens position, and Snowden has every right to not subject himself to a broken and corrupt system