Untrue, or at minimum incomplete.
Grant's wife may or may not have owned slaves. Her wealthy father certainly did and "gave" some to her to help around the house. There is no record of any transfer of legal title, which may or may not have happened.
Whether she or her father owned the slaves legally, they were freed with all other MO slaves in January 1865 by state action, almost a year before 13A in December.
Almost all slaves were freed by Emancipation Proclamation or state action. 13A freed slaves only in DE (about 200) and KY (around 50,000).
More to the point with regard to Grant's attitude towards slavery, he actually legally owned one slave. This was a couple of years before the war. Grant and his family were in severe financial straits.
We have the record of Grant freeing this slave, who could probably have been sold for around $1000, considerably more than the median annual income for the time.
IOW, somewhere upwards of $50,000, in today's terms.
I’m sure its hard if not impossible for you to accept that many many people in the North owned slaves all through out the Civil war. When asked about it Grant was known to have said that it was just too hard to get good help.
Deal with it.