Yeasts will produce all sorts of strange smells while fermenting. A strong sulfur smell is the most common. In a confined space like a closet, any of those smells will be concentrated instead of dispersing off into the room air. Your beer is fine, relax!
If, after fermentation is complete, you have a cidery flavor, your problem would be that your can of John Bull extract was old. Some people try to blame that flavor on the addition of sugar, but that urban legend was debunked years ago.
By the way, adding sugar instead of DME was probably a good idea in this case. John Bull has a fairly high percentage of non-fermentable sugars. The addition of sugar will give you the gravity you want without increasing the unfermentable sugars. You should get a decent FG this way.
Had you used a brand like United Canadian, you would have been better served by adding DME as United Canadian is highly fermentable.
Bugeater Brewing Company