Ok I’ll play.
Fair warning, without being there I’ll have to make many assumptions.
For one, I’ll be nice and say “I think you are mistaken” if the blue arrows represent the ships course on your marked up navionics picture. There’s absolutely no way the freighter was that far north going inside the sailing/swimming bouys off Dunderave. If he was at full steam as you say, and leaving the harbour, he’s most likely loaded which would mean his draft is between 25-50 feet. No chance he’s in 40 ft of water.
Here’s my guess, you are near the middle of his intended route to the normal and charted outbound lane (between QB and half a mile North of QB), you are headed to QB. One long blast is his “nice way” of letting you know he’s there and you’re kind of in his way but doing ok, or it was a short blast letting you know he’s altering to starboard. He’s plotting you and knows how close you’ll get and when, and is altering to starboard to go around you. Uh oh, you turn to starboard. Now his plan to go around you is up in smoke and you get 5 short blasts for the trouble. Now he’s trying to stop altering to starboard, it takes a while because he’s so heavy. You go even faster to starboard and he’s now pissed and sounds another 5. Passes off your stern.
The only other option I see is that he was not at “full steam”, and was actually slowing down to drop anchor in one of the three West Van anchorages and he felt like you were in his way.
It can be deceiving, but a container ship at first narrows coming out will be on you at the QB bouy in 5 minutes. If you draw a triangle from first narrows, to the QB, to a position half a mile north of the QB, this is the area to avoid when you notice a ship coming out of the harbour. Like others have already said, listening to ch 12 takes all the guess work out of it and you’ll know who’s coming and what their name is should you need to call. I would suggest that’s it’s very rarely that a rec guy needs to call up commercial traffic, when most situations can be resolved by taking EARLY action to stay out of the way.