Ack, well we don't want that. Fairly good vibes between us all...
While you can appeal any property, you do not need to be the owner, appealing someone else's is not a good idea vis a vis your relations with your neighbours
The problem is that an error on your neighbours assessment is not grounds to have your assessment lowered.
I would suggest that you call BC Assessment and talk to your local assessor and ask them to explain how this happened. If they see something is not right, they will check the situation out over the summer.
Now there are possible reasons for why the assessments might be different that you have not taken into account. Location and property size matter. Simple things like being on a corner or no, a partial ocean view etc can add 5-10% each to the values.