I’m not sure exactly what Plex considers a “play” for a music item, but it’s definitely not the same as iTunes, which updates the play count if and only if the track reaches its end. Doesn’t matter if you skipped straight there or played the whole thing.
I have a smart playlist of all my unplayed items, which I shuffle to gradually work through. To knock something off the list, I want to actually have to get through it. If I make it partway through a song, but don’t ever hear the second half of it, I don’t want credit for it. I’m sure the current play count behavior has its benefits too, but could there be a setting to change what constitutes a song play count?