They're different... Twitter software engineers get very high pay to do dull work, whereas Tesla engineers get actually impactful work, but very demanding working hours and low pay.
Of the engineers I've met, I'd put the Tesla ones as 'smarter'.
This is strictly re: software engineers but I don't think that's true IMO. Put another way, I think the average recruiter/co-founder/EM would be more interested in hiring an ex-Twitter engineer vs an ex-Tesla engineer.
but I have inspected plenty of organisations where strong engineering teams are drowned by management bullshit. even found places where most of the individuals, engineering and management both, are arguably competent but the overall organisational decreptitude kills any and all effective work, no matter how heroic or skilled the individual and collective effort gets.
Honestly, it's mostly because they pay more. They're more selective and thus have better engineering talent meaning Twitter engineers on the average are going to have a better engineering skills than Tesla software engineers
Tesla engineers likely are drinking the Kool-aid or were not talented enough to get offers at better companies.
Lastly, it's not "just tweets" at their scale. That's like saying Netflix is just storing some video files in CDNs.