In Qur'anic Arabic, "sanat" means a year of hardship or a typical year because life is hard, while "3aam" means a year of ease.
Yes, I’ve read and heard that a lot, but the evidence is pretty weak. The only aya that mentions العام in a positive sense is the one you mentioned, but العام is mentioned 8 times in the Quran, one is positive, 4 times neutral, and twice negatively in the sense of hardship!
فَأَمَاتَهُ اللَّهُ مِائَةَ
عَامٍ ثُمَّ بَعَثَهُ - البقرة
وَوَصَّيْنَا الْإِنسَانَ بِوَالِدَيْهِ حَمَلَتْهُ أُمُّهُ وَهْنًا عَلَىٰ وَهْنٍوَفِصَالُهُ فِي
عَامَيْنِ - لقمان
(The eighth time is still talking about the dead man).
سنة is also mentioned 8 times and also only one is really negative, one of them you can argue that it’s negative, and one is actually positive:
قَالَ تَزْرَعُونَ سَبْعَ
سِنِينَ دَأَبًا فَمَا حَصَدتُّمْ فَذَرُوهُ فِيسُنبُلِهِ إِلَّا قَلِيلًا مِّمَّا تَأْكُلُونَ - يوسف
These are the “good years”, which are followed by the bad ones:
ثُمَّ يَأْتِي مِن بَعْدِ ذَٰلِكَ سَبْعٌ شِدَادٌ
We can assume here that what is meant is سبع سنين, implying that the Quran used سنين either for both the hard and the easy years, or it used it for the easy years only. In either case it contradicts the theory.
There is also no evidence of that in other Classical sources, including dictionaries that mostly just use the words as synonyms.