Glitch in Apple Watch Workout or Fitness app

Hi- I noticed something bizarre today in after my indoor cycle workout. Not sure if this is a glitch in my watch or something in the iOS fitness app. One day I did the indoor cycle workout for 47 mins with avg HR of 145 BPM and it burned 344 active calories. Today I worked out for 48 mins and burned 345 Active calories with 149 avg BPM. In today's workout my avg BPM is 4 BPM higher, and 1 min extra but only 1 additional active calorie. Does this sound like a glitch? Can anyone explain why there's such a minor difference? I've attached screenshots for reference. Thanks