xFi Speed Test Way off from actual speed?

Our plan covers up to 100mbps, but I have never seen anything close to that in my lifetime (at least in our home). I connect my imac with cat7 to xfinity router, so I should be getting more than 100mbps support anyways. Yet doesnt matter who I download from, never have seen more than 15mbps (on a good day). On my phone I dont even bother with wifi half the time, since my data is faster. Well I was gonna forward a port and decided to run speed test.

Its literally telling me Im getting 117mbps (around same twice) and 70mbps (just once). Im so confused our plan is 100mbps. Nothing I mean no download no torrent has ever been that fast. I understand some websites purposely throttle your download speed to keep their server stable. But anyone know whats going on?