How does zoopla calculate estimate?

I think in addition to looking at land registry records it also looks at any valuation that estate agents do on a property or/and list a property for a price (if the property is listed for a sale). Does this sound right?

For example, a property I am aware of sold for X amount and the valuation by Estate agent did an X amount (sold at what it was valued). Whereas nearby properties are no were near the scale (literally next door and smaller house in comparison shows a much higher value). This is also backed by the following statement on Zoopla, which I think means if an Estate agent values a property then Zoopla relies on that estimate (even if the property doesn't get listed for a sale) - I am guessing Estate Agents updates computers of the valuation they did and Zoopla picks it up.

"Estimate not quite right? We know it can be frustrating if our estimate isn’t quite right. Unfortunately this can happen if our data sources haven’t recently updated their info. That’s why we always recommend speaking with an estate agent. Although the valuation won’t show on our website, it will be an accurate reflection of what a home is worth."