Indeed, this stop is mapped differently from other stops in Helsinki; I fixed it and removed public_transport=platform from the waiting area, this is what triggers StreetComplete to ask for details about the platform.

(That being said, to map tram stops properly, the railway=tram_stop node should be attached to the tracks and the public_transport=platform tag should be on the platform area and only there, but that is a major tagging change and I wouldn’t like to change it on the whole network without discussing it first with the local community.)