Well, it really rather isn't. Punks aren't renowned for musicianship and appreciation of finely crafted instruments. Most 'punks' would have little idea of what to do with a Brian May model Gretsch. But making your own guitar is rather garage, if you'd asked me, as garages are often workshops.
I think it was a reference to the crossover between "punk" and a DIY ethic.
Although, in fairness, the concept of "punk" has meant so many different things to so many people. One person's punk is about arrogant rebellion and breaking shit. Another's is about giving a more metaphorical "middle finger" to expectations and striking your own path outside of the more commercial/disposable monoculture.
At least when I was growing up, it was definitely my introduction to the "no true Scotsman" argument, but I think a level of conscious iconoclasm is inherent in any definition.
Consider recalibrating your worldview; you’ll be glad you did. The use of ‘punk’ in this case does refer to the long-standing association with DIY, which is frequently associated with garages and workshops.
Also, punk shows are up-close and personal, so you’ll definitely see names like Gretsch, Orange, Alembic, etc. if you care to look.
Punk is very strongly connected with DIY. Often times you had to do it yourself because money is scarce: printing your own shirts, pressing records, setting up shows, etc.
