Well, to be precise, "reasonable suspicion" is a weaker standard than the "probable cause" required for a warrant. In either case, there needs to be suspicion of something specific, not just "this seems shady".
That said, you are certainly correct that "probable cause" is less than proof, and knowing nothing about the case it seems plausible that "this guy is accepting packages for people he doesn't know" firmed up some link in their reasoning and made the difference between lacking and having probable cause.
That said, you are certainly correct that "probable cause" is less than proof, and knowing nothing about the case it seems plausible that "this guy is accepting packages for people he doesn't know" firmed up some link in their reasoning and made the difference between lacking and having probable cause.