Always consider this - even if you stay with around 2100 cal./day and train hard, it isn't as if fat is magically going to sneak up on you one day and deposit 20 lbs. without notice. You can still eat more carbs and test things, if you find that you're gaining weight too rapidly after a few weeks, then try your trainer's advice and decrease carbs a bit to see how it fares. Look at it this way - if they've been right about everything so far, and have gotten you close to where you want to go, then it doesn't make sense to abandon all they've been teaching if you want to stay the course for progress. You can also SLOWLY increase total calories as well, maybe just upping the total by 50-100 cal./day from your current amount to the higher 2100 total over the course of a few months, thereby allowing better adaptation without as much shock to your system from a rapid increase. Figure this, it's like anything else, if you diet hard and strict for a few months, your system will be in prime "store everything I can because I don't know when I'll get to eat like this again!" mode, which does make fat gain more likely with a quick return to higher calories, so perhaps a slow return is the better approach. Not to mention, along with fat loss, you've certainly had some muscle loss as well, therefore your body will still require fewer total calories per day than it did when you were bulking up at the end of 2011.
I know all too well how it is to be carb-sensitive - too much rice, bread, fruit, etc. all ends up settling extra weight right in my gut, the last place it ever wants to vanish from. Doesn't matter if I stick to "clean" carb sources, once I'm over 400g/day (and don't forget, I'm also 6' tall and 238 lbs.), my fat gain kicks back up and it's back to square one. Some of us really do operate better with fewer carbs and more protein/healthy fat, we're not all the same and there's no "perfect" plan for people to follow that will guarantee things will work out ideally. I know there are tons of vegans who say "Just eat lots of good carbs, don't worry about protein, it'll be great!", but what works for them does NOT work for everyone else, and if I followed such advice, I'd be 300+ lbs. and feeling like crap within a year or two. There's nothing wrong with being carb-sensitive, it just means it's a bit more tricky to fine-tune diets without having to always be more protein-focused.
It all boils down to what you want in the long run. If you want to stay lean and not worry about gaining fat for a while, then play it safer and don't up the carbs too much/too quickly, keep protein high, and change things slowly. If you plan to compete again later and want to gain more mass and/or don't mind dieting down again, then there's no worry about putting a little fat on with your lean mass, it's bound to happen. If you're focused on health completely, then that will likely take you in a different direction. Just think about where the next season's goals lie for now, and plan accordingly!
"A 'hardgainer' is merely someone who hasn't bothered to try enough different training methods to learn what is actually right for their own damned body." - anonymous