I believe (probably non-controversially) that designers are more than pixel pushers. Designing digital interfaces in 2018 without a familiarity with code is akin to a painter hiring someone else to wield the brush, without understanding the viscosity of the paint, how colors mix, or what a brush can and can’t do. The design and the medium are one.
Imagine instead if you were to ask about the error. Instead of making your assumption, you’d say, ‘These numbers aren’t adding up.’ This is a simple statement of fact. Your colleague reacts by saying, ‘Oh, you’re right. I got this spreadsheet from so-and-so in accounting, and I didn’t look at that part of the spreadsheet. I worked on this tab for you.’ That part of the spreadsheet is flawless. Now you have a completely different opinion of this person because you made the effort to understand first. Note the facts are unchanged in both scenarios.