Yes, please don't be alarmed. The blog has moved to a new platform and the comments were moved here into the community site.
There was no announcement because it was not intended for these comments to be visible. There was an unfortunate side-effect of the import process that apparently forced them to be visible. Sorry for the confusion and disruption.
Briefly, I thought my account had been hacked when I read under (My) Comments that I had made a number of posts today. Then I saw they were from contributions I'd made some time ago in the Blog - and now appear in the "Blog Comments" section of Community.
It might have been less confusing if an "Announcement" had been pasted at the top of this category (as such are placed from time to time under the other categories of Community) to advise of this sudden import of hundreds (about 40 pages) of old posts.