Straight upright.Did you check with the bike leaning on it's kickstand, or did you stand it straight upright the way the owners manual says to? It's always going to read low if it's on the stand. If you filled it up to between the lines when it's leaning on the stand, then you seriously overfilled.
I suspect the guy sold you the most expensive appropriate oil he had available.
I don't know oils, but I did read the manual. Good to see you adding to the conversation.
So apart from it being expensive, the question still stands: "is it the wrong type of oil for my bike?"
Based on a few other contributing responses in this thread, some use 5W/40 so I'm just going to ride it and see what happens.