It does not really refer to a smell, but an atmosphere in the kitchen created while cooking. If it was smoky, it would be called smoky, if it was smelly it would be referred to as smelly. Smeechy refers to a smoky atmosphere, as a result of cooking, which creates a stinging sensation to the eyes. Well that is how I have always understood it!
I am from cornwall in the UK. I now live in New Zealand. I have just been in the kitchen with my partner who is cooking the most enormous Steak! Yummy! It has created a smeech in the kitchen! My eyes are stinging slightly! Perfectly cooked steak, but nevertheless a smeechy kitchen! I walked in (oh a kiwi guy by the way), and said "wow, it is smeechy in here!" He had no idea what I was talking about!