It's normal IF the indexing on the data was not optimal, so that you were scanning old data before that has now been removed.
Note that when you DELETE a large number of rows SQL defers the actual release of the data pages until later. A batch process later removes these "ghost" rows in increments. For 1TB data, I guess it's possible that it took more than 2 days to completely DELETE the ghost rows.
You should rebuild the affected tables after that large a DELETE.
You should also review index statistics, including missing indexes and current index usage and table scan counts, to verify whether you need to re-index one or more of the tables.
SQL DBA,SQL Server MVP(07, 08, 09) Prosecutor James Blackburn, in closing argument in the Fatal Vision murders trial:
If in the future, you should cry a tear, cry one for them [the murder victims]. If in the future, you should say a prayer, say one for them. And if in the future, you should light a candle, light one for them.