Is it justified for a Buddhist to believe he could be a real Buddhist only through meditation, and to discard all concerns about serving society?

To be a real Buddhist is just to take the Triple Gem as one’s guide, that is to say, if anyone puts his or her faith in the Buddha, Dhamma and Sangha, he or she is regarded as a Buddhist. This is according to the answer of the Buddha to Prince Mahanama’s question about being a Buddhist.

There is an advice for progress in practice called the Basis of Merit Making as taught by the Buddha as follows:
1. Charity or generosity (Dana),
2. Morality (Sila), and 
3. Development of Meditation which is of two kinds, namely: tranquillity of the mind and spiritual insight. (Bhavana)

From the above mentioned principle it is clear that charity and serving society in the way of giving a helping hand and other spiritual practices are regarded as the additional (practices) of being a Buddhist.