Ok that was a bug and should be fixed. Thank you for mentioning it. The different enemies should spawn in based on a certain amount of time passing to allow you to have unlocked the appropriate counters for them.
But what really defines a clicker to you? All of the elements of a clicker are there, they are just presented in another form. At least in my opinion. Instead of generating your currency immediately after clicking, its more secondary mechanic that results from your clicking. Click to spawn a monster that proceeds to destroy another monster that will then generate your currency. I guess to some extent every game (on pc at least) is a clicker, unless its completely keyboard controlled.
Actually, yeah I agree. I dunno, its probably too involved to be a clicker, and yet at its core its just using clicker mechanics. I guess clickers just basically strip all the additional layers of games down to their most basic form, give me some input and you'll get some output, which this does do, but not without an added layer of requiring a more precise clicking mechanic.