Hi scooby gods...

Please help me understand something about my scooby
It's an s -reg classic with an sti version 2 engine My temp gauge wasn't working. I ordered a new coolant temp Sensor and when I goto replace it I find that the existing sensor Was an oil pressure sensor. When it was unscrewed it looked like An oil well but the temp sensor screwed in just fine.I connected the wire and the gauge now seems to be working.What's confusing me is that the oil pressure sensor I removed is Located directly under the alternator , directly behind that is the second Sensor for temperature that feeds the ecu.

The part is listed as a coolant temp sensor. Could it be possible this car was
Designed to feed the temp gauge from the oil temp??

There is no oil/water mixing as I checked.... Very confused

Any help would be appreciated