No worries.

Mechanic #1 installed the cog/lockring using hand tools. (A chain whip and a lockring spanner)

You rode it for a while and the torque of your legs on the chain may have torqued the cog onto the hub a little harder than the mechanic had originally installed it using hand tools.

Mechanic #2- Checked to make sure the lockring was still snugged down against the cog to prevent it from having any back and forward play in it which could strip the hub over time (ofr all at once if you skidded really hard)

If Mechanic #2 gave it a go-ahead I'd say you should be fine to go ride worry free.