Their observation isn't remotely an ad hominem: They are specifically criticizing the message, not the speaker.

And their point is valid: There is a wide "startup" belief that you needn't know the market or domain, the customers, etc. You just need to find a domain name and make a web page and customers will come and somehow a business will fall together. Only the overwhelming odds are that it will face likely failure.

Another trait of many of these types of posts is what idlewords points out: The tendency for people to generalize lessons. This is the risk of the dirty sushi restaurant with poor service that inevitably fails, but then writes a broad treatise about how the area won't support sushi restaurants. We see this constantly among such "lessons learned", where macro inputs are often substituted for micro failures.