How can the genesis block contain arbitrary data on it if the script is invalid?

[Bitcoin]

How can the genesis block contain arbitrary data on it if the script is invalid?

The coinbase transaction from the genesis block contains this script: 04FFFF001D0104455468652054696D65732030332F4A616E2F32303039204368616E63656C6C6F72206F6E206272696E6B206F66207365636F6E64206261696C6F757420666F722062616E6B73

It pushes the text "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks" into the stack.

I heard that scriptsig is invalid unless there is only one entry in the stack and that entry is '1'. So this script is invalid.

Is this why people say that the coins generated in the genesis block are unspendable?

Source: How can the genesis block contain arbitrary data on it if the script is invalid?