As trophywench says, it's all about perspective.
For a start, the carb count per 100g is largely irrelevant other than for helping you to determine your total carb intake. The idea that everything with less than 10g of carbs per 100g is 'low carb' is a slightly silly one from your DSN. For instance, Coca-Cola has 10.6g of carbs per 100ml - and ml is equivalent to grams for water, so that means a can of Coke is technically on the cusp of being a low-carb item. Something to think about next time you treat a hypo with a regular soft drink!
Now we've dealt with the amount of carbs per 100g as being not particularly relevant, let's look at TOTAL dietary intake. The NHS recommends around 250-300g of carbs a day, so technically, anything under 250 is 'low carb'.
However, the main goal of low-carbing in relation to diabetes is to change your body metabolism from fueling itself on carbs to fueling itself from fat. There's no hard, fast number where this process kicks in. Some sources say 50g. Others say 40g. Bernstein's plan recommends less than 24g of carbs a day, specifically divided into a breakfast and lunch of 6g each, plus an evening meal of 12g. From my personal experience, I start running into difficulty with blood sugar control at more than about 100g, so I can't imagine how anyone with diabetes could eat 300g a day and stay healthy, as that would mean gorging on bread all day.
Interestingly, there's some debate about whether this is such a thing as a 'free food' for T1s. Firstly, protein actually converts to glucose but in a slower manner than starch, so if you eat a large steak, you might think you've not eaten any carbs at all, but you will probably still need to bolus a small amount otherwise your blood sugar will rise about three hours later. There's also a theory that your body also releases glucose in response to food being in your gut. The theory goes that when your small intestine is stretched by a calorific ite, (ie. anything but water), your body sends two signals - one to release insulin in anticipation of digestion, and another to release glucose from your liver in case the amount of insulin released is too much for whatever's in your intestines. Obviously the insulin release signal doesn't do anything in a T1, whereas the glucose release signal does - the end result is that any food in your gut will cause your blood sugar to increase slightly, regardless of its carb content.