It seems like a large part of the ruling hinges on the fact that Google matched the image hash to a hash of a known child pornography image, but didn't require an employee to actually look at that image before reporting it to the police. If they had visually confirmed it was the image they suspected it was based on the hash then no warrant would have been required, but the judge reads that the image hash match is not equivalent to a visual confirmation of the image. Maybe there's some slight doubt in whether or not the image could be a hash collision, which depends on the hash method. It may be incredibly unlikely (near impossible?) for any hash collision depending on the specific hash strategy.

I think it would obviously be less than ideal for Google to require an employee visually inspect child pornography identified by image hash before informing a legal authority like the police. So it seems more likely that the remedy to this situation would be for the police to obtain a warrant after getting the tip but before requesting the raw data from Google.

Would the image hash match qualify as probable cause enough for a warrant? On page 4 the judge stops short of setting precedence on whether it would have or not. Seems likely that it would be a solid probable cause to me, but sometimes judges or courts have a unique interpretation of technology that I don't always share, and leaving it open to individual interpretation can lead to conflicting results.