The two numbers describe different attributes of the device...
The A1489 model number is a generic model/version for this device:
Identify your iPad model - Apple Support
The ME280B/A is the Part Number that provides greater detail, such as its memory and radio configuration (which may be region specific) - and its case colour (32GB, WiFi only, Silver).
I have no idea at all why Apple Trade-In tool might give you a price based upon the Model Number - and not for the part number - unless it only accepts input by model. From recollection, doesn’t the trade-in price tool actually ask you for the device serial number - which is unique to the device?