Why HR has taken this attitude with you in this meeting is something that we can only speculate on, and several answers have already raised various ideas. It is surprising to me that no one has mentioned this: Taking a single day off once in a while could indeed be due to a minor illness. However, having three or four occasions in a fairly short period of time (and a year to a year and a half could be considered short for this), might make the HR folks wonder if you're job hunting and calling in sick to go on job interviews.
If that's their suspicion, they may be trying to find out if it is correct. They may fear that they need to keep an extra close watch on your activities (in case you're one of those notorious disgruntled workers who might try to sabotage the company). Also they may be trying to determine if they need to prepare to fill your position soon ... or if they think it would be better to let you go before you leave.
I'm not saying any of the above is what is happening (or is appropriate if it is what they are thinking), I'm just pointing out the possibility.