I guess you could grapple with 83.1 as to whether the Blues player controlled or intentionally passed the puck back into his defending zone, but it seems that rule 83.2 expands on that to include deflections that are not caused by direct action from an attacking player:
"83.2 Deflections / Rebounds - If a puck clearly rebounds off a defending player in the neutral zone back into the defending zone, all attacking players are eligible to play the puck. However, any action by an attacking player that causes a deflection/rebound off a defending player in the neutral zone back into the defending zone (i.e. stick check, body check, physical contact), a delayed off-side shall be signaled by the Linesman."
The way I read this - and please correct me if I'm wrong - is that UNLESS a Bruins player initiated some form of contact with the Blues player or his stick in the neutral zone, an offside attacking player is free to play the puck. There was no such contact on the Blues player by a Bruins player, thus no offside. Thoughts?