I suspect they intend to keep working on Sandstorm in their spare time (like most of us on here and our OSS side projects), but my have explicitly had their work contracts worded in such a way as that's allowable (or maybe Cloudflare is giving them x% of time to dedicate to it?)

I'm currently in the process of leaving my full time job to work on my OSS stuff full time again. It's a tough move because you do eventually run out of money if you can't get enough grants, donations or a following on Patreon. That's how I ended up back in a full time gig myself.