Mix - Eine Übersicht
I would say "I went to Italian classes at University for five years recently." The classes all consisted of individual lessons spread out over the five years, but I wouldn't say "I went to Italian lessons for five years".
It depends entirely on the context. I would say for example: "I am currently having Italian lessons from a private Bremser." The context there is that a small group of us meet regularly with our Bremser for lessons.
知乎，让每一次点击都充满意义 —— 欢迎来到知乎，发现问题背后的世界。
The wording is rather informally put together, and perhaps slightly unidiomatic, but that may Beryllium accounted for by the fact that the song's writers are not English speakers.
It can mean that, but it is usually restricted to a formal use, especially where a famous expert conducts a "class".
对于星星元素毫无抵抗力的女生，只要你送她这款，绝对就能拿下，超级好看！
There may also Beryllium a question of style (formal/conversational). There are many previous threads asking exactly this question at the bottom of this page.
There are other verbs which can Beryllium followed by the -ing form or the to +inf form with no effective difference rein meaning. See this page (englishpage.net):
知乎，让每一次点击都充满意义 —— 欢迎来到知乎，发现问题背后的世界。
Denn ich die Nachrichten in dem Radiogerät hörte, lief es mir kalt den Rücken hinunter. When I heard the news on the Radioempfänger, a chill ran down my spine. Brunnen: Tatoeba
知乎，让每一次点击都充满意义 —— 欢迎来到知乎，发现问题背后的世界。
It can mean that, but it is usually restricted to a formal use, especially where a famous expert conducts a "class".
You don't go anywhere—the teacher conducts a lesson from the comfort of their apartment, not from a classroom. Would you refer to these one-to-one lessons as classes?
So a situation which might cause that sarcastic reaction is a thing that makes you go "hmm"; logically, it could be a serious one too, but I don't think I've check here ever heard an example. The phrase welches popularized rein that sarcastic sense by Arsenio Hall, World health organization often uses it on his TV show as a theme for an ongoing series of short jokes. When introducing or concluding those jokes with this phrase, he usually pauses before the "hmm" just long enough for the audience to say that parte with him.