I've been hanging out with aerospace engineers for a few years. But, even with basic physics you need to remember: all velocity is relative to a point of reference. When dealing with orbits it gets so complicated that we have to be mentally agile enough to accept that there are many useful reference frames that all make sense depending on what you're observing. Most humans default to thinking in terms of ECEF reference frame so it can be hard to think of other frames and how the relative numbers are affected.