@grantoury That article was discussed at length here: https://forum.cyclinguk.org/viewtopic.php?t=155260&hilit=aluminium+emissions.
Some of the figures are questionable, e.g. 'The most detailed life cycle analysis sets the carbon footprint for an 18.4 kg aluminum bicycle at 200 kg CO2, including its spare parts, for a lifetime of 15,000 km.' But where are the 18 kg aluminium bikes? An aluminium road bike is more likely to be in the 9-10 kg range and that, obviously, makes a difference to the CO2/KM figures. However, even if some of the details can be questioned, the general drift of the article makes sense.
I'm not surprised by that. The article seems to have set out with a particular position in mind, and found evidence to support it. One thing that also occurred to me is from the original article is that the author has a fairly high mileage for each ride (which suggests it's not for utility purposes only) - and one way of making a bike last longer is to do less miles. I suspect a lot of people who use bikes just for utility make them last a really long time. I've seen people commuting on/riding to the pub on what many would regard as knackered old BSOs for years - they might only be doing 1-5 miles slowly each way but it all adds up.