I wouldn't assume that everyone knows about the death of his mother. I didn't until you posted the article. In this case, the comment was relevant to its parent because the parent was adding an anecdote about the number of people they know who had ridden Uber versus Lyft, and the comment was adding its own anecdote about their workplace/coworkers switching to Lyft.

Like I said, I think it depends on context. In this case, I wouldn't say it's tone deaf to mention the CEO of Uber being one of the main reasons you don't use Uber anymore, unless the article is directly talking about something bad happening to him. For example, if the article about his mom's death got to the front page, and people made comments about how bad of a CEO he is or he's the main reason they don't use Uber, that's not ok.