I see what you're saying, but it doesn't make this survey at all convincing. You also have to consider what exactly they're measuring - "reliability" is a very broad term. Model S have common issues with their fancy electronic door handles for example. Doesn't apply to the Model 3 and a rear door handle not working as normal isn't the same as a car being completely unusable!
Depends on their methodology, but if there was no weighting in play, it wouldn't affect the results.
i.e. you might have 50 total Tesla owners respond, 28 of them own Model S, 18 had problems with the doors. Therefore overall they're 64% reliable. Then add in 22 Model 3 owners, 11 of whom had problems with... steering or whatever. Overall reliability is now 42%, that is 42% of Tesla owners who responded had no problems.
It'd make sense if they weighted the results according to the time the car was then with the dealer or a 1-5 rating of how inconvenienced the owner was or something, but without seeing their methodology I've no idea. Personally I think a rear door handle not working is just as bad as a car being unusable. It's a pretty fundamental thing, being able to open doors. I think any issue that requires a trip back to the dealer is significant.