If by highway he meant the section of the East Coast Parkway that is straight and wide (the median has potted plants rather than planted trees), my recollection is that this is a myth, that section of the highway may have been intended for planes to land on in an emergency, but no longer. Unfortunately I do not have sources.

But if by highway he meant Lim Chu Kang road, then it's not just plausible: Lim Chu Kang road is actually used as an extra airstrip. The RSAF conducts regular exercises to ensure it can still be used as such, the last one being about 5 years ago [0]. There is an interesting video from 2009 on the subject too [1].

[0] https://www.straitstimes.com/singapore/planes-taking-over-li...

[1] https://www.youtube.com/watch?v=CBMD4QTSyqM