I mean, yes - but authorities realized very quickly how bad Chernobyl is, and started cleanup operations immediately. International knowledge of the incident had nothing to do with the starting the procedures. It's quite clear from Legasov's tapes that at least in the early days, Soviet Union and its leadership was genuienly interested in containment and cleanup.
So yes, I'm also interested in the same question as op - why has Chelabynsk-40 not caused the same reaction? Was it because it was a military installation?