I mean, the Bold Trait is in fact a distinct, known, thing with distinct effects? So I'm not seeing a contradiction there.
To go into the last time we were warned of ambition (or, at least, the last one I remember):
That's in regards to Folkmarr, but it clearly also indicates that we have it as well. Which means it's either invisible...or it's the Bold Trait. I think the latter, but whatever it is, we definitely have it. Halla probably less extremely than Blackhand, and maybe even less extremely than Folkmarr or our new Skald friend here, but we have it.
The choice to capitalise the name strongly suggested to me that Ambition's Spark is the proper name of something with its own metaphysical significance, different than just regular ambition. Since we've never seen Blackhand use that name used before, logically we've never encountered it. However, reading that quote, it might be that I'm reading too much into the choice of naming and capitalisation and you're right. It would certainly explain the "eerily familiar" if it's meant to be evoking self-recognition.