There are 34 people with the surname Bottas in Finland, so it’s not exactly a common name. While Bottas as a surname can apparently be found in Portuguese-speaking countries, the most likely explanation for Valtteri in particular is that it’s a Swedish name, which are common in Finland. Many farms, particularly in eastern Uusimaa, have names that end in -as, and having the farm name become a surname when surnames became a universal thing in the mid-1800s is possible.
In present-day Finland, there’s a Bottas Alley that leads to a single farm – one of two companies containing the name Bottas in their name or ownership records is still found in the same municipality, while the other (run by Valtteri’s father) is found in Nastola 65 kilometres away, where the driver is from. I’d be surprised if they weren’t related, but who knows.