Locus Walker saw him joining the Lightforged not how he became one.
For all we know he got a lesser Naaru to Lightforge himself counting on the Naaru just trusting him due to him being Lightforged.
Furthermore Xe’ra focused her mind reading on Turalyon whom she personally Lightforged before making her decision on Alleria.
Wasn’t that at the start of Legion though? So it could be possible that he became lightforged prior to Legion.
I meant to say Xe’ra had the ability, and between that and a hardliner she was, I think she would’ve been sus of a Lightforged Nathrezim and subjected Lothraxion to it.
Lothraxion was already Lightforged back when he recruited Alleria and Turalyon into the Army of the Light, and Xe’ra was still active then.
Xe’ra being out of commission with her sentience core sent to Azeroth was a relatively recent development during Legion, so while not definite, timing-wise it potentially was Xe’ra who converted him.