Coastal Karnataka has a lot of Konkani speakers in North Coastal Karnataka & Tulu , Konkani & Beary Bhashe speakers in South Coastal Karnataka . Add Kodagu to it who have their own language.
Then you have Marathi speakers in Belgaum district . Bordering districts to AP , TLG & TN have a lot of Telugu & Tamil speakers respectively. But this is a common pattern across the country where bordering district population are bi lingual but have to state 1 language as their primary language for the census.
What isn't common is the Muslim population almost to a man declaring themselves as Urdu or Dakkhani speakers !
Karnataka is the only South Indian state where native (Kannada) language speakers amount to ~ 65% of the population. This isn't to say the rest don't speak Kannada . It's just how the census records this data which in turn fuels insecurity among native Kannada speakers which is the reason you see them venting against non Kannada speakers in Bangalore mostly.