I mean, who cares? Fire up the gas plants in the one week a year you have weather anomalies. We’d still be 90+% carbon free which would be incredible. The last gap can be solved at a later point as technology evolves
It ignores storage, over-provisioning, aggregation of uncorrelated sources etc.
Not to mention that wind typically has a much higher capacity factor than 10%.
I don't know what the true number is, but I think this is a low effort take.
PV it varies by how far you are from the equator, 10% is realistic for a Northern country like the UK or Germany whereas in Africa you might see 25% or even 30%