What causes Pseudomonas fragi to smell sweet?
The strawberry-like odour that you perceived is mainly attributed to three ethyl esters, namely the ethyl esters of butyric, hexanoic and 3-methylbutanoic acid.

There are other odour-active volatiles produced by Pseudomonas fragi, about 26, which are said to add to the richness and complexity of the odour of the three aforementioned main compounds.

Source:

Analysis of odor-active volatiles from Pseudomonas fragi grown in milk - Cormier et al. 1991

The study by Cormier et al. should be a good starting point for further reading as it references a variety of scientists who have worked on this.