How is this tensorflow command interpreted?
This question is very much about code syntax of the Keras Input layer (Tensorflow backend)...


shape=(100,) meaning - The shape variable takes as input a tuple of integers, not including the batch size. For instance, shape=(100,) indicates that the expected input will be batches of 100-dimensional vectors.
It knows how to deal with "dtype='int32'" because that is how the Input class was written (I have no better answer). The data type variable takes as input a string (float32, float64, int32...).


The official documentation of the Input layer: tf.keras.layers.Input

This link has all the answers you are looking for.