Two power sources on gas furnace?
Furnaces are required by code to have three shutoffs:

An emergency shutoff located outside the area of the furnace
A service shutoff located on or near the furnace
A switch, breaker, or fuse located at the electric panel

The emergency cutoff only interrupts the burner supply circuit, while the service shutoff will turn off all electric power to the furnace, which is why they enter at different locations. My best guess is that during the previous owner's demo, they moved the emergency shutoff closer to the furnace for &quot;convenience&quot; and removed the &quot;unsightly&quot; red &quot;OIL BURNER EMERGENCY SWITCH&quot; plate.
As Steve Wellins mentioned in comments, this was mostly likely not done by any trained and professional electrician, and is most likely not up to code.
Source: https://inspectapedia.com/heat/HVAC_Power_Switches.php