This year the ninth day of the month of Av fell on Shabbat. Since fasting on Shabbat is forbidden, the holiday of Tisha b'av (which literally translates as "the Ninth of Av", hence the confusion) was pushed back to the following day, and is observed on the Tenth of Av on the calendar, as required by the relevant halacha.
This excerpt from Halachipedia provides the relevant info, citing the sources I've copied below:
When Tisha BeAv falls out on Shabbat or Sunday
Delaying The Fast
If Tisha B'av falls out on Shabbat, it is pushed off until Sunday and everything that would be forbidden on Tisha B'av is permitted on
Shabbat.  According to Ashkenazim, some hold that relations are
forbidden on Shabbat which is Tisha B'av unless it is her tevilah
night. On the other hand, according to Sepharadim, relations are
permitted on Shabbat.
If Tisha B'av falls out on Shabbat and is pushed off to Sunday, one may eat meat or drink wine on Monday day and not Sunday night. 
According to some poskim, one may even eat meat on Sunday night. 
One may, get a haircut or do laundry immediately on Sunday night. 
If Tisha BeAv falls out on Shabbat and is pushed off until Sunday, according to Sephardim, a pregnant woman or woman who is nursing may
eat on the fast day. Nonetheless, they should not eat for
If Tisha Beav falls out on Shabbat and is pushed off to Sunday then there is a dispute among the poskim as to whether or not a boy who
becomes Bar Mitzvah on the 10th of Av is required to fast.
Havdala on Motzaei Shabbat
If Tisha BeAv falls out on Shabbat and is pushed off to Sunday, the bracha of Boreh Meorei HaEsh upon a fire is made on Motzei Shabbat
before the reading of Eicha (while Boreh Mineh/Isbeh/Atzeh Besamim is
omitted), however, the bracha of Havdalah on a cup of wine is
delayed until after Tisha BeAv, Sunday night.  An adult who is
exempt from fasting should recite Havdalah on Motzei Shabbat before
eating. One may fulfill his/her obligation to recite Havdalah even
through someone who is permitted to eat on Tisha BeAv.
If one needs to eat on Tisha B'av that falls out on Sunday must recite Havdalah beforehand but they should wait until they need to eat
to recite Havdalah and not say it immediately Saturday night unless
they need to eat then.
Shulchan Aruch O.C. 554:19, Kaf HaChaim 554:86, Yalkut Yosef 556:1