well - for anyone coming behind me that wants to do this - I commented out the button on the _ProductBox.cshtml file - because I could not find the "DisableBuyButton" setting
The DisableBuyButton is on the ProductVariant admin page, there is a checkbox DisableBuyButton. Otherwise if you want to disable the buy button across the whole web site, instead of editing all you product variants, you can go to Configuration -> Access Control List, and there is a permission Public store. Enable shopping cart, which you can set on the appropriate customer role. However since you would like to disable it on the category page only, I believe your solution is the only one.