The Constant1 block has its Output data type parameter set to Inherit: Inherit via back propagation. Because the Constant1 and Constant blocks are both connected to the Data Type Duplicate block, the Constant1 block can inherit its data type from the Constant block. The Sum block has its Output data type set to Inherit: Same as first input, so it is also able to inherit its data type from the Constant block.

If you change the data type of the Constant block from single to int32, the int32 data type propagates throughout the model.