These numbers are 538s polls-plus forecast. Polls-only is slightly worse but getting better every day.
Silver has his opinions, but primarily what he does is produce models that analyze polls in a very sophisticated manner. The models are somewhat constrained by the very fact that they use polls, but if one wants to keep up with the polls at all, I don’t know of a better site than 538.
Polls-plus is more favorable because it includes economic data that historically favors the out party.