This article should answer your question
Just in case you don't wanna read all that:
Reference cards basically means the manufacturer of the card makes it aka NVIDIA for GTX RTX etc. and AMD Radeon Vega etc.
Non-reference cards are by the partners of AMD / NVIDIA examples being EVGA ZOTAC GIGABYTE etc.
Best assumption I can makeSo pretty much Gigabyte is showing the MHz of the reference card to compare with theirs for people to see.
the reference design is everything about the card. the circuit board layout, power needs, speeds and even cooling. generally most brands make a full reference design card and then changes the cooling a number of times while still using the same basic circuit board (called a pcb) most of the bottom half of "custom" cards are simply reference pcb's with custom cooling and a small overclock.
the card you asked about is actually one of these. a reference pcb with custom cooling and a slight overclock.
then there are the top end cards that are custom pcb's as well. these tend to have much beefier power delivery abilities and are over-engineered to the max.
you can tell what is what by looking at the reference specs usually found on the nvidia/amd product page and then compare it to the card you're looking at. if they have the same power phases and power needs, then it is likely a reference pcb. if it has more, then it is a custom pcb
there is nothing wrong with a reference design with custom cooling but know what you're getting so you don't overpay. no reason to spend an extra $100 for custom cooling that the card really doesn't need due to lower power used. but $25 for better cooling is almost always worth it so the card is not bouncing off thermal limits the whole time.