They are referring to market share. 10% market share of the market for intelligent mixers sold in a year in Spain is not the same as
"About 10% of Spanish households have them." now is it?
10% market share of which market???
40 million Spaniards, 10 million households, approx 125,000 units sold a year (250,000 units sold last year and this year alone). Thermomix has been around for way more than a decade, so even in previous years with lower sales one can assume that 1 million units have been sold in the Spanish Market over the past 20 years.
10% of households.
And from the source quoted above:
"Y eso parece cuando se pregunta a los propietarios del aparato, presente en 1,6 millones de cocinas en nuestro país."
There is a Thermomix in 1,600,000 Kitchens in Spain