There’s a few confounding factors to address before you get to the believability of the claims (which are remarkably dubious). For starters they’ve only spoken about the AWS region which is least reliable by design (as it is the first to receive new features), and they’re talking about a 10 year time span (AWS in 2010 was much less reliable than it is today). It’s also not really clear what they’re talking about when they say AWS. If it’s just the core features you’d need to forklift an on-prem service into the cloud, then the claims are especially frivolous, but the SLA difference between EC2 and AWS Ground Station is more than an order of magnitude.

Even if their claims are true (which I certainly don’t believe they are), you’d be more likely to get better uptime than EC2 with a small on-prem setup through dumb luck rather than through deliberate planning. Something still has to go wrong for you to have an outage, and you’re more likely to get an incredible lucky streak than you are to outperform their entire AWS infrastructure capability with a few people and half a rack of servers.