Maybe they intended to deice on a remote area,it's a common thing at big airports.
Few days ago we had to deice on BRU ,a somehow long taxi to the deiceing area,then deice with the engines running.
Of course there could've been some restless pax on the plane,seeing us leaving the gate and taxi with ice on the wings,and thinking I will take off like that.
You did alright,but my guess they would've deiced anyway.
Brgds Alex