It's also the only source that publishes. Oryx documentation indicates direct photographic evidence for 50% of the numbers listed here and when you consider that most Russian losses are in areas not easily photographed by civilians this is a strong indicator these reports have some basis in reality. That said, I agree these numbers should absolutely be taken with a grain of salt.

the source (UA general staff) is obviously biased, yes, but we don't know how good or bad it is yet

here's the original source (yes it's facebook): https://www.facebook.com/GeneralStaff.ua/posts/pfbid029Hp57mafK62hrb2gQMqQfL8inL45TErQCHSSQWgsBBGvLQZGW7u275LDutt7QZpJl