Reason for the apology was no big deal. A seat change happened which did not upset me and I understand things happen. The lead FA said she wanted to send miles my way for the inconvenience, and 15k was the highest level available to her on her device. Shortly later, an apology email followed indicating the 15k:

Please accept 15,000 SkyMiles, along with our heartfelt apology and commitment to be better for you and all Delta customers. Your compensation should be available for use within four to six weeks. If you do not receive your SkyMiles after six weeks, please contact us at www.delta.com/contactus.

Okay, so 4-6 weeks for the miles, but in fact miles have already been deposited. But Only 5k. Is that apart from the 15k? SM account calls it a customer service bonus. So that means 5k + 15’??

Maybe I answered my own question.