Kit producers say lots of things. Their goal is to get the consumer to get beer made quickly so it can be consumed quickly so more kits can be purchased. Not all of their comments are actually aligned with making better beer.
There are a number of reasons this could have happened. Due to all sorts of things, temperature, etc, your yeast could have dropped out early on, and then slowly rebuilt itself back up and did its thing. OR You could have gotten an infection which is fermenting some stuff that the beer yeast did not ferment. OR something else could have happened.
Leave it alone, let it finish its new fermentation, then give it another few days or so, maybe an extra week. Then bottle/keg it, let it hang out a bit, and drink it.