Don't understand what physical appearance has to do with tech.
Professional companies are stereotyped to suits and ties, and company attire is often part of company dress code.
Tech companies are stereotyped to kids and what they wear, and company dress code (if it exists) is often super-lax except for executives -- because the executives need to interact with Professional companies and look the part.
There's a lot of in-between, and it really depends on what company you work for and somewhat to what company you want to work for.
They’re not saying that how you look impacts your real ability; or vice versa.
People think of ability as just technical, or just soft. It is mixing it all together that produces true strength.
If I wear a suit at the wrong time, it shows an inability to read the room, and in some firms may even have gotten my manager to ask if I was looking for a job!
So, understanding how to dress how you want to be seen is critical. I'm not saying it's high fashion time, but at least understand the audience, and the aura you want to put out.