It`s an old traffic method but it does work. Not that I do it anymore. But back in the day I did make some interesting connections with it, getting to know people and their blogs.
I prefer to be the content creator and focus more on delivering value than trying to skim off others value.
But it`s not really spamming you are adding some value. It`s just low value content generation.
I think most blog comment forms have a "website " field for a reason, though. There's a tactic quid pro quo there. Leave a comment, add value to the discussion, maybe a few people will click on your link. And the vast majority of bloggers I know are happy to get comments. A well-placed comment on an unknown or up-and-coming blog can make the author's day.
The impression I got (and the impression I get as a blog owner) is that he was leaving a link within the comment body, as opposed to the URL field. People do this all the time on my site and it sort of immediately invalidates their comment for me.
I prefer to be the content creator and focus more on delivering value than trying to skim off others value.
But it`s not really spamming you are adding some value. It`s just low value content generation.