Any moisture in the tank will combine with ethanol and sink to the bottom. If your tank wasn't completely full when you left it, I guess it's possible moisture in the air above the fuel level condensed and was absorbed into the fuel. This combined with the same effect in the fuel bowl might result in this mixture being in the carbs at 1st start.
TBH, I'm a bit of a doubter about E10 being quite as serious an issue as sometimes reported, but I avoid it whenever I can. There are plenty of reports that fuel stabilisers don't actually do much. But whenever it's raised, there's usually anecdotal responses to the contrary. I don't use it, myself andvthe sky's not yet fallen in.
My garage does get a fair bit of condensation over the winter. I find my carburettor bikes are slow starters, but then run fine. I ride my bikes on dry days throughout the winter. I've always had to clean carbs when I first get my bikes, but never had a problem afterwards.
