The difference is that it wasn't hard to work out the claims were nonsense. WMDs are
hugely expensive, and the Iraqi economy was running on fumes at that point. That combined with US belligerence against Iraq made the claims improbable.
But Russia actually does have a strong black hat culture, with links to the political establishment. Putin is a technologically savvy kind of despot who likes sneaky low-cost high-return actions. So this fits the profile - both as a workable hack and also as a proof of concept for future attacks.
Consider the cost/benefit. Instead of physically blowing up infrastructure and security systems you can cripple them, possibly permanently, for the cost of - what? - 20 or 30 specialists, some PCs, and maybe some supercomputer time. Although even that may be optional.
It's unlikely conclusive evidence will be released, because that might reveal too much information about defence strategies. So circumstantial evidence will be as good as it gets.
But whatever the cause, clearly - clearly - all countries and larger orgs need to work much harder on security. Some decorative pen-testing isn't going to be nearly enough in the 2020s.