They're abusing the notation, but doing so in a way that's perfectly clear.

I also didn't get it.

so I think in their notaion O(10) has greater magnitude than (>) O(1)

You're expected to read it out loud (in English), where one of the conventional readings of O(f) is "order of f". Conveniently "order of 100" is usually taken to mean not asymptotic behavior bounded by a constant multiple of 100, but a range within an order of magnitude or so of 100.

Which is to say, they're saying Deno has a cold start time of ~100 ms, package size ~10M, a physical machine can support ~1k instances.

cool, it is good to know but, at the same time, it is weird. I would use x convention to deliver that message. That comparison table is there for a reason and that is to deliver a marketing message. I'm sure there could be some better ways to deliver that message.