This claim comes from BioMed Research, a trusted publisher that puts out peer reviewed studies. The claim that chewing gum helps with focus is backed up by the content of the study.
"Chewing gum has enhanced sustained attention performance in previous research [3, 4], consistent with an alerting effect of chewing gum [4–6]. There is some evidence that this effect may be moderated by time-on-task, with the ameliorating effect of gum being greater following a long period of performance [6, 7]."
In addition, an academic article from the University of Newcastle supports this claim with similar findings.
"Chewing gum can be an inexpensive and effective way to help relieve anxiety and boost attention."
https://www.newcastle.edu.au/hippocampus/story/2023/can-chewing-help-manage-stress
This claim appear to be true.