RJ45 is a kind of a historical accident. It originally referred to a telephone company wiring standard. Common 10/100/1000 Ethernet wiring uses the same physical jack, but a different wiring. But since the jack was the same, it took the name. So now
RJ45 basically refers to just the jack. Technically, it should have been called 8P8C, but it is what it is.
So when they say
RJ45, they just mean the standard Ethernet jack that all common wired devices have. A regular Ethernet cable will connect correctly to that jack.