Let's take the following company. The current ETH Balance is
But API response
As you can see API response does't contain floating point so the balance value is very big.
Is it bug?
it isn't a bug the balance is returned in weis not in The Ethers.
chek one of many conversion tools: https://etherconverter.online/
268705.32703842675 Ether = 268705327038426745609145 wei
"," is used to separate three digits (look at the amount in $).