The source is ADS-R and UAT.
So you are receiving it directly on 978 MHz via UAT.
On 1090 MHz there is a ground-based repeater that is rebroadcasting the position of that plane as well, that is categorized as ADS-R. (doesn’t mean the plane you see is a ground based transmitter, just that the information is coming from one)
As such, depending on reception and maybe some insufficient handling of that situation on my part, it’s flipping between two data sources. (it should at least if i understand my own code correctly, not flip if you receive an UAT position often enough)
Technically UAT isn’t a data type as it’s just ADS-B transmitted over a different data link.
But people like to see what they receive via UAT, that’s why i made this crutch in my interface even when it’s technically inaccurate.
Btw, your question belongs in the thread about tar1090 (customized interface for dump1090-fa).