United B789 weird config

I am flying United on their Dreamliner in Economy Plus. Seatguru states there are two configs of the aircraft type (one fitted with Premium economy and one not). Both can be found here.

For my flight, I see my seat numbers (21A and 21C) are labelled as Economy Plus but going by the numbers and the seat arrangement, it appears weird. Has anyone come across this United airlines Dreamliner config?

PS: I am not sure if this is the right place for the question. If it is not, could someone let me know where can I ask this question.