Note this is not a comment about the quality of Lambda School. I've heard good things about it. But it's almost tautological that someone shouldn't be eligible for a "senior software engineer" title after they've graduated Lambda School, just as they shouldn't be eligible for it after they've graduated university. Such training is necessary but insufficient for being able to meet the level of responsibility you're given at that title.
Like I said, this isn't a comment on the Lambda School. It's a comment on the idea that this occurrence isn't absurd, regardless of whether or not it's rare.
Senior Engineer is a relative title. It means more senior than the other engineers at that firm not other engineers at different firms. A senior engineer on the google android team is way more knowledgeable than the senior architect at a local coding shop where the average dev makes 40k/year and has a year of experience.
The "Senior" hires may have significant outside industry experience, even if they only have 9 months of programming experience.
The title is a paygrade in this case, not a level of experience.
You can imagine how well this went over.