the reimbursement for a downgrade under EY261 is now based on the fare for the segment fowngraded (rather than the previous 'ticket price') was result of an EU court case that excluded taxes and airport fees from the calculation (as in general these are the same no matter what cabin you are in). IIRC carrier fees / surcharges were also excluded.
And yes they can (and do) hide part of the ticket cost by increasing the 'carrier surcharge' which isn't part of the base fare but is part of the ticket cost.
In this case the downgrade was on two short segments (and I'd doubt the downgrade on the intra US leg comes under EU261) t and so the reimbursement would be very small.