The whole article demonstrates a much wider problem that exists in more places than just Silicon Valley. As a whole, startup founders have little experience actually running a business and even less running HR policies. What is acceptable and what isn’t.
This line though, is somewhat symptomatic of the problem. Just for our understanding, was this acquaintance not well known to you or had you known them a while? Acceptable behaviour is totally defined by how well you two got on. For example, when networking it is in essence, possible to generate a non-monetary trade of one professional favour for another. In that context, to take you out for drinks (as if on a ‘date’ or friends hanging out) if he didn’t know you well and you were not friends, was inappropriate. By contrast, if someone does know you well, you get on well, and do hang out outside work, then it’s not so out of the ordinary.
It’s precisely that blur of the lines which make some people assume an appropriate situation when it definitely isn’t. Some indeed hide behind exactly that.