Why is the mold inside of my Samsung Galaxy S9+ USB charging port?

[Android Central Question]

2 days ago I got the "Moisture in the USB charging port" error message. I've had the device for 4 months.
I live in Ensenada, MX on the Eastern edge
Relative humidity is usually low, recent rains temporarily raised rel. humidity for a few days.
Phone had 28% charge
After I got the message:
I unplugged the device and waited while 3 hours passed.
I plugged the device in and got the error msg again
I unplugged the device and, I blew air
Using a hairdrier (set to high and held 12 inches from device) I dried it for about 5 minutes.
I dried the charging cord using the same technique.
I plugged the device in again and again got the moisture error msg.
I set the device upright in a box of kleenex overnight (powered up)
I plugged it in and got the moisture error msg again.
Device has 15% charge
I unplugged it and held down the PWR key and the VOL UP/DOWN keys simultaneously. The screen went black and the device would not power back up.
A trip to Telcel (they SUCK) TO FIND I've got MOLD in the charging port.
HOW IN THE HELL could mold have gotten into the USB charging port? There's metal and plastic in there.
+THERE WERE NO FOOD PARTICLES IN THE PORT+
Any ideas? I'm stumped.

 

[Kodak2]

If you carry your phone in your pocket that would be a likely source of the contamination, but only you can really identify the source.