If it doesn't say "ALKALINE" then it isn't. Nobody wants to admit their batteries are carbon zinc, so they call them "heavy duty" meaning they have 14% more power than a 1940s regular carbon-zinc, a.k.a. "general-purpose". Nobody (AFAIK) makes regular ones anymore, presumably because nobody will buy them willingly.
It's like organic food. Nobody wants to buy inorganic or industrial or imitation food, so they invent terms like "natural" which have no legal meaning, in the hopes that you will mistake it for organic which does have legal requirements.
I think I forgot to mention that carbon-zinc cells have a very short shelf life - never buy them as surplus no matter how cheap!! - and they leak gooey corrosive paste eventually. Oh, and did I mention I think they are obsolete crap?