The San Ġwann Observation Post does not appear on any available historic maps as a defence post. The slit windows do not appear to have been designed for the use of rifles or automatics weapons by troops inside. One would expect loopholes to give fields of fire.
In 2016 there were plans to demolish the building which was described as a pillbox. The developers seem to have built over and around the structure.
The images here are from 2016 before the site was developed.