This is not very high quality data. Extrapolating from the cases I know about, I wouldn't be surprised if half the deals on it were merely nominal acquisitions. You would have to have some threshold on the size of the acquisition for the list to be meaningful.
Looking at the locations of companies acquired in small deals is particularly misleading as a measure of the clustering of startups, because smaller deals are generally done as an alternative to series A rounds. So they're disproportionately likely to happen to startups that don't have access to funding.
For example, YC funded one startup that had an acquirer appear on the radar screen about a week after they closed their series A. That had priced them out of the acquirer's reach (for now). If they'd been located outside the Valley, the startup would not have been able to raise money so quickly, so the acquisition might have happened.
Looking at the locations of companies acquired in small deals is particularly misleading as a measure of the clustering of startups, because smaller deals are generally done as an alternative to series A rounds. So they're disproportionately likely to happen to startups that don't have access to funding.
For example, YC funded one startup that had an acquirer appear on the radar screen about a week after they closed their series A. That had priced them out of the acquirer's reach (for now). If they'd been located outside the Valley, the startup would not have been able to raise money so quickly, so the acquisition might have happened.