My wife is also T1 diabetic. In principle, yes, a major airport's medical team should have everything that a diabetic needs to survive. However, depending on the person's blood sugar level at any given moment, it may be necessary to give them either insulin or sugar immediately or they will become disoriented, unable to move reliably, and maybe pass out. Hypoglycemia and hyperglycemia can quickly become medical emergencies. Given all that, it makes sense for a diabetic to be highly protective of their insulin and sugar supplements. In a crash, the medical team is probably going to be pretty busy and might not provide optimal treatment to a diabetic right away.

A "pancreas kit" can fit in a bag small enough to be carried in one hand, so it shouldn't be necessary to hold up an evacuation by carrying something large. As others have mentioned, this is also likely an instinctive reaction, and it's hard to criticize someone for reacting that way in such a stressful situation.