Except that figure shows the frequency with which PV46 experienced an interruption, not the frequency with which it was near an interruption. As stated in the article, "We could not inspect the detailed train logs that day because SMRT needed more time to extract the data", implying that there was no position information for trains that were not actively experiencing a disruption.

Arguably, based on the preliminary explanation, it seems like PV46 might be over-represented (it had 4 interruptions) -- after all, it never travels in the opposite direction to itself.