Yes, because again how can you know what to expect out of something you've never seen before?
Several trainers have had this happen to them throughout the course of the anime and no one is immune to this, Ash has had it happen to him a few times such as Gary's Electivire after the battle frontier, when Pikachu had just taken down a Regice, but Electivire made short work of Pikachu because Ash didn't know what it was capable of.
there's also another factor to consider to these arguments about Dragonites "Ice" resistance in the past.
It's likely that when fighting Beartic and Mamoswine, Dragonite had prepared and braced itself to take those moves despite them being weak to them, yet with Dracovish it's guard could've been dropped due to the shock factor and thus that's why ice fang worked so well.
let me use this as an exmaple, say you got in a fight with someone and you are about to get to punched, you know it's coming, and if you brace yourself for the impact the damage is likely to be lessened even if it hurts because your focusing your senses towards it in preparation, but let's say the puncher does something shocking that drops your guard and makes you lose that focus, all of a sudden that punch is likely going to hurt alot more because your no longer as prepared to take it.