We all produces pheromones anyway, Dr Chapel could've simply been commenting on that--that the Ilia-Probe was so complex as to include something so small as BO.I'm curious. Did we all just forget the scene in TMP in Sickbay. Where the Ilia probe is being examined by Dr McCoy and Chapel. Chapel comments that even she noticed her (Ilia-probe). The examination showed that the probe had replicated Ilia's pheremone function using microscopic pumps. Kirk commented that if Ilia had been replicated so perfectly and completely that the probe might be suceptable to emotional influence from Decker.
As for Decker's reaction, he had just witnessed the woman he was madly in love with die on the Bridge before being brought back to him--so his overwhelmed reaction is pretty understandable I find.