I ran small recruitment agency for one year long (never again! terrible sharks industry). During that time I saw many non-ethical tactics used by other agencies. Some recruiters would do what you explain for one of the the following reasons:

a) to blackmail the company in the likes of “I won’t touch your employees if you recruit using my services from now on”.

b) already had a signed agreement with your employeer which didn’t allow the recruitment agency to “touch” any of its employees. You seemed like a match for their new client and the recruiter was checking if your employer agreement was still valid. Of course, this is also seen as blackmail by companies.