I would mostly agree he is a box to box midfielder, yes he does attack, against some teams more than others. I never said they play with 2 dedicated defensive midfielders who sit in front of the defence the entire game. I said
from what I've seen of West Ham this season (and Moyes teams in general) Soucek and Noble will often sit deep as their starting position. They'll try to keep it tight and then hit teams on the counter, this is when Soucek attacks and probably gets most of his goals (as well as from set pieces).
I could be wrong as I don't watch all their matches, but a quick check on which positions he's played this season on Transfermarkt says this.
33 games, 28 Defensive Midfield, 3 in Central Midfield and 1 as an attacking Midfielder.
https://www.transfermarkt.co.uk/tomas-soucek/leistungsdaten/spieler/283628