"Sampler??"

Gentlemen,

I'm in the process of trying to track down a fault in my main HP spectrum
analyzer. I've narrowed the issue down to the area of this "sampler" which
is part of a phase locked loop. I'm not sure I fully understand its
function, however. In particular, I'm extremely confused as to why they're
calling it a "sampler" because when that term arises, I typically think of
something doing akin to what a sampling oscilloscope does: noting voltage
levels at predetermined intervals. AFAICS, this "sampler" is doing no such
thing. It's just a harmonic mixer, surely? If not, I must be nuts. YOU get
to decide!

Block diagram here: https://disk.yandex.com/i/YXcGssgDXwVEbg

Short functional description here:
https://disk.yandex.com/i/k7YTYTGjHltsGw