Chances are you’re just now figuring out what your max HR is. Years ago when I first got a HRM I spent some time seeing how high I could go… I found that I only hit max HR outside and on all out 1 minute power tests (basically every time I hit max around 40-45 secs). Then I found I hit similar numbers at the end of some races. I have also had some variability with HR straps, and need a few weeks of training to figure out if any deltas are real or just the new HRM.
My HR is always higher outside… I’ve even done 20+ minute TT’s in the summer with higher average HR than some of my max HRs on the ramp test. I feel like on the ramp test I stop from other fatigue before my HR has a time to get to max, but I’m sure everyone is different.
I also agree with comments about freshness and that it is something you can get better at the more you do. You need decent fitness to push yourself that hard without stopping, so agree with above that it is a good sign that your fitness is improving.