It's the strong emotional reactions in threads like this that get me. Is it really such a triggering thing to say that there isn't some truly terrible sin here, but just a simple regrettable misunderstanding to be learned from?
And there's so much unspoken conflation happening as well. How do handshakes or "grabs" relate at all? I mean, yes, they are forms of touch, but in another league altogether from a momentary hand on the shoulder. Like ya'll are imagining 90% this, rather than relating to actual occurrence.
All that said, the thing about not touching as a general rule of thumb is on the money. The more difficult part, and where most misunderstandings come from, is the hazy gray area as you're getting to know a person when you may make mistakes about the level of expected intimacy, which is all about context and upbringing.
When mistakes or misunderstandings happen in the hazy middle ground of knowing someone it can be difficult to to get back on the same page, but still, there should be some reasonable space for working out the misunderstanding. IE, apologizing, and moving on.