A friend called me selfish for taking a quiet walk while I have covid. Was I really wrong?

Currently in the UK you are not required to isolate at all if you have covid although it is recommended. I tested positive over the weekend and stayed at home. However, I was feeling a bit better today so I went on a quiet rural walk to get some fresh air as my legs had been getting really stiff from sitting in bed and I also have no garden to sit in. I purposely went to a really quiet area where I knew I wouldn't encounter anyone - and I didn't. Even if I had, it would have been spacious enough for me to have given them plenty of space away from me.

But when I got back, a so-called friend of mine sent me scathing messages saying that I shouldn't be going out and that I was really selfish for doing so. I have already notified work that I won't be going in due to covid and I won't be doing any shopping or mixing with people so I don't understand how I am really being selfish- I was literally walking in rural fields. Was it wrong of me to go for a rural walk? Her comments have really bothered me because I'm honestly not a selfish person and I think that's a horrible thing to say to a friend.
A friend called me selfish for taking a quiet walk while I have covid. Was I really wrong?
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