First premise: The frogmen knew of their connection with Steve.
Second premise: The frogmen weren't worried about people with JANIG connections.
This might be explained by superior weapons in the hands of the frogmen, coupled with the assumption that the Spindrifters had no communication with Steve. It might also be explained by knowledge of their real reason for being on Clipper Cay.
Rick didn't care much for the last two premises. The first one seemed more reasonable. After all, they were not sure that the former tail had seen the Water Witch in St. Thomas, or had known of their connection with it. On the contrary, to get to Clipper Cay so soon after the Spindrifters arrived, the frogman must have left about the same time the scientists did. There was even a possibility that he had arrived ahead of the Spindrift group and that the frogmen's boat had been out when Rick and Scotty had first spotted the diving equipment in the house. Anyway, there had been no sign of any tail but the Virgin Islander while they were around the pier and on the Water Witch. Either he or Scotty would almost certainly have spotted a second man—especially since they had seen him before.
There was a major precaution, however, to be taken: he and Scotty must not let Steve's former tail get a good look at them. They had to assume he had recognized their clumsiness for what it was—a deliberate stall.
Scotty poked him, and Rick suddenly realized that he had been leaning for quite a long while on the broom he was supposed to be using.
"Made up your mind about anything?" Scotty asked.
Rick knew his friend had been watching him. During their many adventures each had developed a rather unusual understanding of how the other's mind worked.
"Partly," Rick replied. He told Scotty his thoughts.
"You make sense," Scotty agreed, then added practically, "but I don't see what difference it makes, whether they know about our connection with Steve or not. The moment they catch us snooping they'll assume we're enemies. Until then, they'll let us alone just as they've been doing."