While importing a page on a wiki where an account doesn't exist a SUL autocreation is triggered. Such these autocreations are logged by checkuser extension under importer's IP/UA. This kind of behavior produces pure noise which should, IMHO be avoided.
This is related to T44345 in that in both cases, the IP that should be used should be an invalid IP (such as 127.0.0.1) indicating that this is something the server is doing, not something a user is doing.
We have a patch for that (https://gerrit.wikimedia.org/r/#/c/92050/) which would allow overriding the IP address of an RC event, but it is still stuck in code reviewer. @Legoktm created that patch, and I encourage him to revisit the patch and respond to the review comments (by me). Once that is in place, we can hopefully use the same strategy in Special:Import and/or SUL code to override the IP there as well.