That is a distinction that was invented by the state.

Calling yourself an "engineer" is unspecific, and is not a claim to authority, but to knowledge. To claim that it is suddenly a specific claim to authority is to redefine the term.

When you redefine a common term, and punish someone for not knowing you did so, that is a real problem. In this case, that was simply done to delegitimize him, which is clearly malicious.