Eckhart Tolle is a spiritual teacher who is influenced by Christianity and Buddhism etc. Now he says that there are Buddhists who claim that his teachings are not really Buddhist. But in what way are his teachings not really Buddhist?
If you call something Buddhism it will be attributed to the Buddha and should be inline with the doctrinal system the Buddha taught. If something is not what the Buddha said then it is wrong to miss attributed something to the Buddha as this is what the Buddha taught. A summary of the majority of Buddha's teaching is encompassed in the Wings of Awakening, 3 Marks of Existence, 4 Noble Truths, Dependent Origination. So if what Eckhart Tolle writes does not have these aspects and if what is found in line with the doctrinal system then you cannot call it Buddhism.
Also some of the core teachings of Christianity and Buddhism are not compatible with each other, so any philosophy influenced by both is neither Christianity nor Buddhism.
There are also Christians who claim he doesn't teach Christianity very well either. Instead, he draws off sources the general public would typically understand. Eckhart Tolle and his teachings are more Taoist than Buddhist. His favorite book to read is the "Tao Te Ching" by Lao tzu. He explains this in his talk called, "Eckhart Tolle - Tao Te Ching and a previous global evolutional era". Although he has very similar teachings to Buddha, he neglects the primary teachings such as the Four Noble Truths, the Three Gems, the Eight Fold Path, and so on...
I've read Eckhart Tolle's book "The Power of Now: A Guide to Spiritual Enlightenment" and if I compare it with Buddhism, I would say Tolle is teaching some form of samatha meditation, that might help someone reach the first or second jhana. Being established in the jhana is being present in the "now" in my opinion.
The experience that Tolle had, which he considers to be enlightenment, is probably just the piti, sukha and samadhi experienced in jhana. I think those who are familiar with Buddhism could read Eckhart Tolle's Enlightenment Story and come to their own conclusions.
Of course as we know, there's a lot more to Buddhism than attaining jhanas. In fact, being addicted to jhanas could be an obstacle to Nirvana.
In his book, he talks about focusing on breath or sensations in the body. These are of course, samatha objects of meditation to induce concentration.