Honestly just anti-foss rambling. Nothing is stopping them to make a custom hardened kernel with what they need. What they want is someone else to cater for them.
ELISA (Enabling Linux in Safety Applications) Project announced that Boeing has joined as a Premier member, marking its commitment to Linux and its effective use in safety critical applications. Hosted by the Linux Foundation, ELISA is an open source initiative that aims to create a shared set of tools and processes to help companies build and certify Linux-based safety-critical applications and systems
I imagine this means they're contributing both actively and financially to Linux.