Tea contains oaxalates which are a main component of kidney stones. However, most studies indicate that you would have to drink a ridiculous amount of iced tea to cause stones to form. I think he probably just developed them through usual means, did a little internet research and convinced himself it's the tea.
I've been using it pretty consistently for several years now. I think something about Lemmy attracts the type of people that use interrobangs, rather than Lemmy creating a culture of interrobang use.
I got that advice as well -- the explanation given to me was that it's almost always used incorrectly, so just be safe and don't. However, I like the way it makes writing more closely resemble natural speech; we usually talk in conjoined clauses rather than complete sentences.