It was a German-designed and built submarine. Nothing backwards about it technologically.
Diesel/electric submarines are not technologically inferior to nuclear submarines. Modern diesel subs are every bit as sophisticated and some ways more, as ours. The German Navy's Type 212A has hydrogen fuel cells in addition to its diesel engines and can stay underwater for three weeks without needing to snorkel to recharge batteries AND is quieter than anything we make. In addition, those same fuel cells can generate O2 as a waste product.
The max of 10 days of air/oxygen is in context of being trapped on the ocean bottom. I don't know if this particular submarine has the ability to make O2 from water, but since it only takes electricity to do so I'm sure some diesel-electric subs do.
An American nuclear sub disabled on the ocean bottom with a scrammed reactor is just as fucked as any diesel with a dead/dying battery. So much for our technological "advantage"
As a matter of fact, the seas last week off Argentina were massively high and the weather was a full on south Atlantic storm. Be that as it may, neither you nor I were there to make the call to remain submerged. And neither do you know what orders was the captain under.
In case you missed the US Navy collisions megathread, I was highly critical of those ships crews because I KNOW they fucked up. How do I know? Because, as a former Surface Warfare Officer, I was trained and qualified to stand bridge watches on surface ships, and I stood them at all hours of the day and under many different conditions. I was not a submariner, so I'm not going to apply the same level of criticism to something I was not trained and qualified to do.