The same thing has been noticed in the past on a regular basis with tickets for TAP, Air India and Ethiopian (especially the first two were always showing availability in first on Aegean's award search, I think someone mentioned one or two cases with Turkish as well at some point).
Anyway the Lufthansa error is present ever since the award system came back to life about 2 months ago and it has shown "first" for flights on the 747-400 as well as the A350 (which is what this flight is on) ever since. Besides the "I" fare, which does mean business class and doesn't change when switching options from business to first, the other obvious error is the "first" ticket costing "only" 75k miles, when there's a first leg on a short-haul jet, which obviously doesn't offer first class. I live for the day, when Aegean's booking system gets a bug or a loop hole (or even better a complete policy change!), that will enable booking of a mixed cabin at the (very fair) price of the more expensive cabin of the two (instead of the sum of their individual cost, which is what they actually charge).