Yes, sure. In a normal computer, the differentiation between data and executable is done by the program being run. Humans writing those programs naturally can make mistakes.

However, the rules are being interpreted programmatically, deterministically. It is possible to get them right, and modern tooling (MMUs, operating systems, memory-safe programming languages, etc) is quite good at making that boundary solid. If this wasn't utterly, overwhelmingly, true, nobody would use online banking.

With LLMs, that boundary is now just a statistical likelihood. This is the problem.