So… they lied?

Eh, yes and no, like this is a longstanding thing with reporting losses/kills in military engagements, everybody over reports kills and underreports losses. A known example is that during WWII in the Pacific, japan zeroes that retreated would throw the throttle to a bit of a overload max in a way, and doing so would cause the engine to smoke a lot. The thing is that to the US pilots a plane smoking that badly was as far as they knew was going to go down, and so they reported those smoking retreating zeroes as kills, then at the end we find out that the US navy killed significantly more planes then what Japan had.

So even without any ulterior motive of propaganda, over/underreporting tends to happen a lot if not all the time in any military conflict.

Edit: If you want a funnier example, how many Tiger Is did the US army see and engage on the western front in WWII? If we take the words of tankers as truth, nearly every time they saw and engaged a german tank (especially if there was a long gun Pz IV in the fight), in actuality it was only three times.