Its on a different frequency. The CW "HUJ" is on 4628 not the buzzer frequency of 4625. It still might be somebody in Russia screwing with all the people who seem to devote their lives to monitoring this boring station. I would think if it was actually buzzer related it would be on the buzzers frequency.
btw the buzzer is a number station? I would categorize it as a utility station. just sayin'