Sometimes federal agents are criticized for „creating“ a crime instead of investigating one. Sting operations are examples of crimes that are a consequence of law enforcement actions. Agents create a fictional crime to trick a suspect into attempting to join that crime, thereby creating the crime.
Similarly, Flynn’s crime of lying to government agents was the consequence of the government agents‘ investigation of Flynn. If there was no crime before Flynn’s interview, then there’s little reason to interview Flynn as part of a criminal investigation, unless the agents were looking to create a crime.