Two years isn't all that long, so I'm not really surprised at your result. I think the typical feedback given on this forum regarding storage in a closet (interior, away from direct sunlight) is that up to two years is ok. So thanks for verifying that!
I would worry about wines in a basement such as yours that I needed to lay down for 10-20 years. Any chance of you performing that experiment?
FWIW my passive cellar goes from about 50-72F over the course of the year. It's a gradual shift as the seasons change, no dramatic spikes either way. I've been storing wine in there for 11 years now and have yet to find a bottle which I thought was even remotely aged prematurely, although I have not done any side-by-side comparisons described above. In a way it's disappointing for me because a little accelerated ageing might allow me to buy more of the 2015 Brunello when released.