It appears to cover the brief period between Emperor John I Tzimiskes' conquest of parts of northern Palestine and their loss following his death and the resulting civil war. This was part of a broader resurgence in Byzantine power in the 10th/early 11th century following the decline of the Abbasid Caliphate. From Wikipedia:

"In 972 Tzimiskes turned against the Abbasid Empire and its vassals, beginning with an invasion of Upper Mesopotamia. A second campaign, in 975, was aimed at Syria, where his forces took Emesa, Baalbek, Damascus, Tiberias, Nazareth, Caesarea, Sidon, Beirut, Byblos, and Tripoli, but they failed to take Jerusalem. He died suddenly in 976 ...Tzimiskes was succeeded by his ward and nephew, Basil II, who had been nominal co-emperor since 960."

"The internal strife quelled, Basil II turned his attention to other enemies of the Empire. The Byzantine civil war had weakened the Empire's position in the east, and the gains of Nikephoros II Phokas and John I Tzimiskes had been lost to the Fatimids."

I don't think the Empire ever really controlled those territories during that time, merely occupied them as part of a war.

There are actually two answers to this question:

1 - The graph is not accurate

2 - The graph would still be inaccurate even if this were the Opposite Universe.

The empire at the time was ruled by Basil II, of the Macedonian dynasty, and at this date the empire did launch offensives against places within the modern-day borders of Syria and Lebanon, and conquered towns like Shaizar and sacking cities like Tripoli, but this would not be in the region we would call Palestine.

As can be seen from this map, even the original Roman province of Palestine/Judaea was nowhere near the Byzantine advances:

http://www.unrv.com/provinces/judaea-map.php

References:

A History of the Byzantine State and Society, by Warren Treadgold.

Thank you both for the answers. I also learned that Byzantium had co-emperors, so that's a plus.