It would be a design mistake that I'd be a bit surprised nobody doing Swedish military contracting would have thought of; but seems plausible enough: aluminum has a fairly high coefficient of thermal expansion(markedly different from glass, which ranges from 'lower' to 'much lower' depending on the formulation); and specialized vacuum tubes remain the image intensifier of choice, thanks to their sensitivity, despite being fairly delicate(and nontrivial to just put a cushy mount around unless you are OK with your scope not being aligned for any length of time.
The glass or the aluminum would be fine; but the idea that a delicate glass tube inside an aluminum enclosure might end up feeling a little squeezed and reacting poorly seems quite plausible. You'll notice that, in aircraft, there's often quite a lot of gasket material around windows as well as the distinctive rounded edges (ask the de Havilland Comet how using nice, stress-concentrating corners went for them); and, in general, a fair amount of separation(also for acoustic and insulation reasons) between the outer aluminum skin, which does flex in response to pressure and temperature changes and internal components(and often dictates the service life of a plane, since the metal fatigue would eventually creep up on you).
It's not like aluminum is an unworkable material at chilly temperatures or anything; but glass/metal combinations are not really a lovable area of material science(thanks kovar, for making it more bearable); and optics you want to stay aligned for targeting purposes make the 'elastomers and big sloppy tolerances' school of tolerating dimensional changes a much harder sell.