Experienced rower, beginner runner question

For the past 7 months I've been rowing on the water for on average 120-180 minutes per week (even in the freezing cold!). As a result my level of fitness and stamina has massively improved to the point where most sessions I don't feel exhausted like I once did. From this training and diet I've lost nearly 3 stone (half during my time on MyFitnessPal).

Over the weekend I tried running outside for the first time in approx 2 years . I don't enjoy running and rarely use the treadmill in the gym, but I wanted to challenge myself. I was shocked that I couldn't run 2 miles without having to occasionally stop to catch my breath.

I concluded that either:

A. My body has become conditioned to one particular sport
B. My technique is poor, including breathing and stride length
C. I'm not built for running

I suspect maybe its a combination of the above.

Anyone else experienced a similar result or suggest ways I can improve my running?

Thanks,

Mike