The little "rumbling" right before the CA/central flag and/or sometimes you might see it before an OA flag is the ResMed FOT...Forced Oscillation Technique that it uses to help decided if the reduction in air movement it is sensing is because of a central or obstructive type of apnea event.
explained on page 8 of the manual I linked to below. Do you have a copy of the clinical/provider manual? If not here it is. https://sleep.tnet.com/home/files/resme ... -guide.pdf
The FOT are little tiny sort of pulses...no where near the burst of air needed for central therapy.
Your machine can't do the burst of air because it can't increase fast enough or high enough. Central therapy would involve a machine going from maybe 10 cm to 22 cm in about 15 seconds or less. None of the regular autoset machines can increase that fast...and they can't go above 20 cm.
Your centrals do seem to be "real" mainly because the breathing around it looks like normal asleep breathing. Awake or semi awake breathing is much more irregular .
You might find this thread helpful since you already like zooming in on stuff and in this thread are links to other interesting threads. viewtopic.php?f=1&t=114600&p=1110933#p1110933
It is normal to have a few centrals get flagged that are real centrals. Sleep stage transition or sleep onset centrals are normal to see. Not a problem unless we see a whole lot of them or the continually bounce a person out of sleep to an awake stage.
Of course sometimes we can have SWJ centrals were maybe an awake/semi awake pause in breathing gets flagged.
Obviously you didn't have nearly enough centrals to cause for worry. I would just shrug my shoulders and move on. Nothing you can do about them with your machine and there's no need to do anything about them with so few of them anyway.