They specifically said they "added an extra shower" and it cost 12k.
My mother just had a quote to entirely rip out her existing 1980s bathroom and refit entirely and the quote came to around 10k.
Personally I wouldn't take them literally.
I know I comprehensively refurbished a en-suite last year at around 8k. The company told me it would be 12k at the moment and with a 6-8 month waiting list couldn't estimate the cost at that time because prices of materials were rising all the time. Then the shortage of labour etc. A lot of people are choosing to refurb or extend instead of moving. Which feeds into the price rises.
Bathrooms in rentals have a hard life.