Looks like they use SmartZip's system. Checking in on the neighborhood I lived in near Philadelphia until last year...
Yeah, that's bullshit. I sold a house there last year and it underestimates its price by $100,000 because its data on it is horrible. The house next door it has at tens of thousands higher than the actual sale price of my former house for what I assure you is no good reason.
ETA: Redfin has a system where it will help you select the most reasonable comps.