If your table is approaching transaction ID wraparound, autovacuum will process it regardless of whether it's turned on or off globally, or for that table. This is one of the many reasons why running with autovacuum off, rather than tuning it to run smoothly all the time, is dangerous. If you haven't done that tuning, and just turned it off instead, when autovacuum does start anyway to deal with wraparound it will not be adjusted appropriately to avoid interference with any activity going on.