As I understand from G.K. Chesterton's Orthodoxy (1908), the Christian God is separate from nature and the cosmos: a refuge and solace separate from the turmoil of nature. "That transcendence and distinctness of the deity ... was really the only reason why any one wanted to be a Christian." In contrast, a pantheistic God is immanent in nature, perhaps in a cosmopsychic mode.
"While pantheism asserts that "all is God", panentheism claims that
God is greater than the universe. Some versions of panentheism suggest
that the universe is nothing more than the manifestation of God."
Focusing on the OP's quote, with some more context from the SEP on Panentheism:-
Utilizing resources from the tradition of German Idealism, Jürgen
Moltmann developed a form of panentheism in his early work, The
Crucified God in  . . . Moltmann moves away from a Hegelian
understanding of the trinity as a dialectical development in history
(J. Cooper 2006, 251). The relationship between God and the world
develops because of God’s nature as love that seeks the other and the
free response of the other (Molnar 1990, 677). Moltmann does not
consider creation necessary for God nor the result of any inner divine
compulsion. Instead creation is the result of God’s essential activity
as love rather than the result of God’s self-determination (Molnar
1990, 679). This creation occurs in a process of interaction between
nothingness and creativity, contraction and expansion, in God. Because
there is no “outside” of God due to God’s infinity, God must
withdraw in order for creation to exist. Kenosis, or God’s
self-emptying, occurs in creation as well as in the incarnation.
To elaborate on this in a modern context it is necessary to pass through some Kant.
“Thus all the possibility of things (as regards the synthesis of the
manifold of their content) is regarded as derivative, and only that
which includes all reality in it is regarded as original.”
As rendered by Tang Huyen who also relates it to a quote from Heidegger:-
if B comes from A, A must not have what B has
“Being cannot be explained through the beings”
(Sein nicht durch Seiendes erklärt werden kann),
(Sein nicht durch Seiendes erklärbar ist). B & T, 251, GA 2 275.
So above are four analogues, with the withdrawing panentheistic God now aligned to 'Being'. What can this 'Being' mean?
The Cartesian answer proceeds from pure reason; that which can be ascertained by thought alone. The scientific answer uses practical reason, insofar as it can.
In pure reason (phenomenology) the existence of things requires the involvement of cognition. Things that 'are' are beings, whether living or inanimate, but the experience of living is a higher order of being. In Heidegger's development of Kant, 'thought' is a product of time and (yet another) more primordial 'Being'.
In the scientific view, 'Being' is that whole state of affairs upon which time can operate to produce thought.
In the phenomenological view one cannot step back earlier than thought so the foundation, so to speak, is unobservable. 'Being' withdraws.
Even in the scientific view, "that whole state of affairs" is an open-ended idea containing many mysteries (including the origin of the Big Bang), and to a large extent is a loose hypothesis in thought rather than a conclusion of physics.
So this "X withdraws" is a way of describing the state of nature, as obtains, right up to the point at which cognition takes over and starts naming things for itself, from which point the actual and unknown "state of nature" has withdrawn and is a mystery to cognition. The panentheistic God or 'Being' is a label for 'the mystery'.
Returning to the OP's question: "Does this mean that [the panentheistic] God is real?" Unknown or unobservable things are only real to cognition insofar as they are 'unknown or unobservable'.
It is worth noting that the buddhist aspiration to quell thought brings one closer to simply Being, and is called nirvana. In Taoism it is suggested that by this simplicity "the virtue of all men would begin to display its mysterious excellence". Chuang Tzu, X